Index out of range in .NET 4.5

Hi,

We have a project that use in .NET 2.0 and it works. However, when we upgrade it to .NET 4.5, it shows following error when we do the record deletion.

Microsoft jscript runtime error
Sys.WebForms.PageRequestManagerServerErrorException: Index was out of range.
Must be non-negative and less than the size of the collection.

But, it works in .NET 2.0 and we can insert & modify record successfully.

Can anyone help us to solve this problem?