This error message typically occurs when a user does not have Microsoft's .NET framework set up correctly for their machine. The necessary components are also provided with PAC-Designer, and can be manually installed by running the file "vcredist_x86.exe" which can be found in the PAC-Designer installation folder (typically 'c:\lscc\diamond\1.3\pac\' for PAC-Designer 6.1 or 'c:\PAC-Designerxx\ for previous versions).