I recently upgraded to grin++ v0.6.1 for Windows. I mine on Grinmint and I withdraw from the pool via file method. The wallet recognizes in incoming file and generates a response. When I upload the response to grinmint I receive an error that the file is invalid.
@quentinlesceller tracked down the issue, and added a patch to libgrin on the Grinmint side to resolve the incompatibility. I’ll make some additional changes in Grin++ 0.6.2 just for good measure, but you should be good to go now.