Recently while deleting a service application my system got unresponsive and while trying to create the service application again i constantly got the following error.
“An unhandled exception occurred in the user interface.Exception Information: An object of the type Microsoft.SharePoint.Administration.SPIisWebServiceApplicationPool named "SearchServiceApplication" already exists under the parent Microsoft.SharePoint.Administration.SPIisWebServiceSettings named "SharePoint Web Services". Rename your object or delete the existing object.”
This seems to be happening because one of the service application pools were not removed while deleting the service application. This can be removed by using PowerShell.
First load the SharePoint 2010 Management Shell by navigating to Start –> Microsoft SharePoint 2010 Products –> SharePoint 2010 Management Shell.
Then use the “Get-SPServiceApplicationPool” command to view all the existing service application pools.
Get-SPServiceApplicationPool
Now use the “Remove-SPServiceApplicationPool -Identity SearchServiceApplicationPoolName” command to remove the service application you want removed. If the service application pool’s name is having spaces remember to use double quotes.
Remove-SPServiceApplicationPool -Identity SearchServiceApplicationPool1
PowerShell will ask to confirm the deletion, after confirming the action, it will remove the service application pool.
d. Select the site or the farm to backup the entire SharePoint farm.
3. Save the site config file.4. Now you need to edit the web applications’ web.config file. Normally this can be found under Drive:\Inetpub\wwwroot\wss\VirtualDirectories\VirtualDirectoryFolder(C:\Inetpub\wwwroot\wss\VirtualDirectories\82)using NotePad or Visual Studio. 5. Find the line maxRequestLength and add executionTimeout in to it as shown below.
6. Save the application config file.7. Do an IIS restart and then your change will be in effect. 
3. Click on SharedServices1 (Administration site host) link in Manage this Farm’s Shared Services page to open the Web Application General Settings page. 
4. Find the Maximum Upload Size property and change it to the maximum upload file size you want. Note that you can put file sizes up to 2GB (2047MB). 
Now you will be able to upload larger files than 50MB.
In the Authentication Providers screen first make sure the correct web application is selected. If not, select the correct application using the drop down in the top left corner of the page. 
After selecting the correct application click on the Default zone (Please note that here I am going to change the default zones’ authentication. If you are to change in another zone simply select the required zone).
As of the result of changing the authentication providers the Web.Config file will be changed accordingly automatically. But this is not enough we need to enter the membership provider details ther in site Web.Config file and Administrator site Web.Config files. 
SharePoint Administration Site Web.Config 
As the final step you have to change the site collection administrators. For this click on Site Collection Administrators under SharePoint Site Management in Application Management.
After verifying the selected application enter Primary Site Collection Administrator as AD:Administrator. If you want you can fill in Secondary Site Collection Administrator as well. After finishing click Ok. 
Now go back to the site and try to login, you will see that the traditional windows login page is replaced with a simple login web page. Since this login page is too simple I did some improvements to the login page and created my own one as you can see below.
b. Select ASP.NET Web Site as the template, select C# as the language, and give a file system location and a name (prjFirst) for the project before pressing Ok. 
c. Now we need to add a page to write our code. To do that, right click on top of the project and click on Add New Item…. 
e. Now you need to use the required web controls and write the code required in the appropriate files. For this demonstration I will put a label and a button only. When the button is clicked I will display a greeting message in the label. 
h. Now build and see if the page is having any errors. If no errors step one is done.
b. Select Class Library as the template under C# project type and give a location and a name (clFirstWebPart) before clicking Ok. 
c. Right click and delete the Class1.cs file since we would like to create a new class with a meaningful name. 
then select Class as the template and give an appropriate name (csFirstWebPart.cs) and click Add. 
e. Now you need to refer System.Web namespace. To do so right click on project and click ok Add Reference…, then select the System.Web and click Ok. 
f. After inheriting the class from the WebPart override the CreateChildControls method to create a user control and load the user control we create earlier in step 1. 
g. Now build the project by right clicking on project and selecting Build. If no errors occur then that means we have completed step 2 as well. 
ii. Go to the root folder of the web site (C:\Inetpub\wwwroot). Now find the folder named UserControls and paste the copied two files there. 
Notes – 
· If the UserControls folder doesn’t exist you can create it there. 
ii. Go to the root folder of the web site (C:\Inetpub\wwwroot). Now find the folder named bin and paste the copied file there. 
Notes – 
· If the bin folder doesn’t exist you can create it there. 
b. Click on Web Parts under Galleries in the Site Settings page to open the Web Part Gallery. 
c. In the web part gallery page you will see all the added web parts. But not our one. So we need to add that here. To do this click on New button. 
Note – 
e. Now our new web part will appear in the Web Part Gallery. This is enough but it is always better to change some properties of the web part. So open up the web part property page by clicking on the Edit button. 
Change the Title, Description and the Group of the web part and press Ok. 
f. Remember that we need to test the web part before we add it to a web page. To do this simply click on the web part. 
g. If you are also having the default settings then you will definitely get an error of request for the permission of type…. This is because we didn’t change the SharePoint trust level. To change this I will use the easy way of changing the trust level in the configuration file to full though the best way is to create a trust file. 
Do an IISReset and refresh the internet explorer page. Now the web part will be displayed to you.
b. Now on any web part zone click ‘Add a Web Part’ button. 
c. Among all the web parts listed select the web part that we have created (First Web Part), select the check box in front of it and click the Add button. 
You will see the web part appearing on the page. 
e. Click on ‘Click Me’ button and see the output. 
Even though adding a new web part was bit of a process, after adding doing changes to it is not that difficult. What you have to do is change the ascx and ascx.cs files and copy the new ones to the UserControls folder. I have simply changed the message to a new one using this method.
Arjuna's space 