Hello!
Hmm, it sounds like you were able to work around the error by removing empty folders and a symbol from your file. The error with empty groups in Sketch files should be fixed on the latest build of the Sketch plugin (0.9.1 as of now). If you’re on that build and were getting an error with one of the symbols in your project, then we’d be interested in taking a look at a copy of the Sketch file that has that symbol if you’re willing to email it to support@axure.com. Thanks!