Have you used ProConnect Tax to file WI returns for nonprofit in previous years?  I'm not so sure it's support.  According to this article, under Exempt, you'd see that very few states are supported in this module.

Before you ask, yes, I know the link is for Lacerte but ProConnect Tax uses the same engine.  Anything not support by Lacerte will also not be supported by ProConnect Tax.

https://proconnect.intuit.com/community/electronic-filing/help/lacerte-e-file-agency-approval-and-st...