I guess that you are launching the SDK from Vivado using the corresponding option, isn't it? Could you test that SDK is working fine on its own? So just open SDK from Windows menu an use a simple workspace path (i.e. C:\workspace).
If that works then just try to open the workspace created by the vivado project (<vivado project>/<vivado project>.sdk)
Ibai Don’t forget to reply, kudo, and accept as solution.