You receive an "InfoPath cannot start Microsoft Visual Studio Tools for Applications" error message when you try to add managed code to an InfoPath form by using VSTA in Microsoft Office InfoPath 2007

When you try to add managed code to a Microsoft Office InfoPath form by using Microsoft Visual Studio Tools for Applications (VSTA) in InfoPath 2007, you receive the following error message:

This problem occurs because the number of characters in the folder path plus the file name exceeds the path and file name limit for VSTA. The maximum length for the path and file name is 127 characters.

This behavior is by design.