Installed Enterprise Developer 2.1 for Visual Studio 2010, however when trying to load a COBOL project it says 'the project file cannot be loaded' in the Solution Explorer of the Visual Studio IDE.

When starting up Enterprise Developer via one of the recent projects on the Start menu, the following error message is displayed:

Micro Focus Visual Studio Host

Error Loading Plug In:
MicroFocus.COBOL.Sql.Rex.ApplicationAssessmentUI
Could not load type 'MFSqlRexComn.ApplicationAssessmentSecurity'
from assembly 'MicroFocus.COBOL.Sql.Rex.Common, Version=4.0.0.0,
Culture=neutral, PublicKeyToken=0412c5e0b2aaa8f0'.

Check to see if Enterprise Developer for Eclipse is installed.  If so, then was it installed before Enterprise Developer Team Edition for Visual Studio 2010?

If so, then un-install both the Enterprise Developer for Eclipse and Enterprise Developer for VS, then reinstall Enterprise Developer for VS before re-installing the Enterprise Developer for Eclipse.  If it's done in this order it should resolve this type of error.