Are you having issues with your Solidworks installation and receiving errors about .Net framework? The issue may be in the Microsoft .NET framework installation. To correct this issue:
1. go to add remove programs and remove any .NET framework installations listed.
2. use a registry clean up utility that will clear any old registry entries. There are several applications that will do this several of them are even freeware. The reason this step is listed is that the registry sometimes retains information even after the application is removed. If this step is not done then there is potential that one of the old registry entries will be used instead of the correct entry which could result in still having the same symptoms even on a "new" install.
3. using your Solidworks DVD. Browse to the folder PreReqs/dotNetFx and run the install dotnetfx3.exe (for 32 bit installations) or dotnetfx3_x64.exe (for 64 bit installations)