We are currently evaluating this issue.
This can happen if an apostrophe is used in the page name of the page that the Mini Donation Form (beta) is being used on.
Please try the following:
1. Log into NetCommunity as a supervisor
2. Edit the donation page
3. Click the green "Page Properties" button
4. In the window that opens, remove the apostrophe from the "Page name" under the Page properties heading.
5. Save and refresh the donation page and try to submit the donation again
If this does not resolve the issue please contact support.