If you’ve read through various migration HOW-TOs, you might’ve noticed a suggestion to turn off batch compilation and rebuild your project to see if any compilation errors come up. This is a very important point as the
Here’s what an MSDN article suggests:
Open the web.config file and turn batch compilation off and re-compile that application to see if any further compilation errors might exist. This can be done by setting the batch=false attribute in the compilation tag as such:
Important: The batch=false attribute should only be added to find such errors and then reverted once any additional compilation errors are fixed. Leaving batch=false in the compilation section has significant performance impact on build times for the application in Visual Studio 2005, so make sure you remove this attribute after doing this check.
More reading on this subject:
Don’t run production ASP.NET Applications with debug="true" enabled
Beware Of Deploying Debug Code In Production