Thanks for reporting that bug, we should have a fix for it in an upcoming release. The most common reason for that error are field issues. Do you have fields being saved to the repository with your form? If so, are any of them longer than 40 characters? The default max field width in the repo is 40 chars so long form fields may fail because of that. If not that, do your fields have other restrictions like lower limits? Regular expressions? Anything else? If the form field value doesn't meet the conditions, the save will fail. 

If you find that's the issue, update your metadata field from max width of 40 to something high enough to accommodate the form value. Retry the save to repository so it will work. Then you can choose to keep the higher limit or change the metadata field manually and put the field limit back. 

In general, it's best to set your form fields to the same character limits as your repository fields so Forms cannot collect values that won't work in the repository.