Visual Studio 2008 CAS / Security settings

I have a windows service that along with several other projects (class librarys) make up a solution. The service also references the Quartz scheduler (from soundforge) and NValidate ( these are not in the GAC)

When I try and view the security settings for the service I receive the following error:

"Visual Studio was unable to determine the Code Access Security (CAS) permissions that are applic开发者_如何学Cable to your project. The most likely cause is that your project references a strongly-named assembly that defines custom permissions, but that is not properly installed in the global assembly cache (GAC). To correct this, try the following:

1. Ensure that any custom permissions defining assemblies referenced by your project have been properly installed to the GAC. If any of these assemblies have been rebuilt or have had their version numbers modified, you must install the new assemblies in the GAC.

2. Restart Visual Studio."

I have looked into the suggestion in point 1 of the error and cannot see any occurances of this.

What else could cause this issue ?

Thanks in advance

It turns out that one of the projects had been changed using VS2010 by another developer which had changed the "ToolsVersion=3.5" to "ToolsVersion=4.0" within the .csproj file.

Changing this back resoloved the issue.

Hope this can help someone else !