Sorry, I have not seen that error before, so I can also only guess. Some ideas/questions what might have gone wrong:
Do you have full administrator rights?
VS sets some variables when it is started for the first time. Did you open it before trying to use it from Dymola?
Changes to environment variables like PATH sometimes require a restart. Did you you restart?
Googling the error message gives many results, e.g. this one:
Maybe try some of the solutions suggested on Stackoverflow?
In the end, it is not a problem with our library, but with your VS installation.
GCC should also work for large parts of our library, everything that is pure Modelica should work.
What does not work with GCC is the netCDF weather data reader, because it uses external DLLs and these would have to be compiled with the exact same compiler that is used for compilation of the Modelica code.