After creating an Ajax web part using a TabContainer, I started getting errors after I added an AutoComplete Extender. I had made sure that the extender is working for a asp.net page.
The problem was that I was using the code this.Controls.Add to add the extender to the Controls collection of the page. The error went off after I changed it to the tbCurrent.Controls.Add, where tbCurrent denotes the TabPanel where I had the TextBox.
After you deploy a new ajax enabled web part and try to run it, if you get the above error, copy the ‘System.Web.Extension.dll” to the bin directory for your sharepoint site.
Suddenly you start receiving errors in the page with no clue whatsoever. By default, sharepoint supresses all the stack trace and ASP.NET ‘yellow’ dump page. (we call it the ‘yellow devil’ 
). To enable it, do the following:
Change the following entry in web.config of the site, by modifying the line…
<SafeMode MaxControls=“200“ CallStack=“false“…
to…
<SafeMode MaxControls=“200“ CallStack=“true“…
and set the custom errors to ‘Off’ .
<customErrors mode=“Off“/>
Problem: When you try to preview an InfoPath Form which has web service data connection, you get an access denied error.
Solution: Make sure the form is trusted under “Tools –> Form Options –> Security & Trust”.
Update: Screen Shots added as per request!
One of the challenges we faced while building an Employee directory with SharePoint is to have an Alphabetical search function. (No, no, I am not talking about using the User Profile to build the Employee Directory. This is purely a user maintainable list)
All the contacts are entered into a single list and when the user clicks the corresponding Alphabet, it should filter dynamically and show the corresponding ones. Ok, you can do that by creating individual views for each alphabet, but that would end up in a lot of work if we want to change something.
Hence, the approach we took is as follows:
1. Create a calculated column ‘Alphabet’ which will be the first alphabet of the First Name. For beginners, you can use the function =LEFT([First Name],1)
2. Create a new View with the columns you want to display (say ‘AlphabetView.aspx’).
3. Open this in SharePoint Designer and convert this into an XSLT view.
4. Right click the DataView, select Properties and create a new parameter, say ‘Alphabet’. Set this parameter to take from the QueryString (say ‘Alphabet’)
5. In the DataView Filter, select ‘Alphabet’ as column name and value as ‘Alphabet’.
6. In the Alphabet links, make sure you pass the QueryString value along with the page name.
e.g. http://abcd.com/Lists/Contacts/AlphabetView.aspx?Alphabet=A
Now if you go to your view from the browser, it will filter the rows by the Alphabet!!!!
If somebody wants screenshots for the above steps, please let me know, I will modify this entry. Screen shots added.
URl Field (Hyperlink) cannot contain more than 255 characters. Make sure the Url length is less than this value (sob! sob!)
New SSP Site creation takes a long time and the status shows as ‘Provisioning…’ but nothing happens!
This rescued me!
http://blog.camantrix.com/sharepoint/2008/04/sharepoint_services_timer_serv.php
One of the typical problems we have when we deploy an Association/Initiation/Task form for Custom Workflows
When we try to open the form during a workflow the error ‘Form not found, this form has been closed’ comes.
Most likely reasons for this:
1. After you designed the form in InfoPath and publish it, you might have changed the Name to make it more meaningful! 
. But you copied the ID for the form from the original form and placed it in the workflow.xml
2. Forgot to copy the file to the Feature Folder.
Problem: You have defined a custom profile property and while trying to obtain this value through code, the value returns null.
Possible Reason: Check the “Default Privacy Setting” in the “Edit Profile Property” Page. Set this to ‘Everyone’ to be able to view/update this.
Problem: While creating a new list definition with Event Handler in Visual Studio 2008, the events are not triggered.
Reason in my case: In the ListDefinition.xml, I modified the “Type=” from the Visual Studio assigned one to a value of “10001”, since that is what MS recommends to avoid clashes in future. If you change the value here you need to make sure you change the value in the “schema.xml” also (in the “<List” tag)!!!