Try the following:
IMPORTANT! Remember to return to the page once you’ve signed in MitID. Only then will your signature be accepted.
Make sure you are using your MitID username to log in (and not, for example, your CPR number or another password).
Reload the page and try again. Read more about technical issues here.
Check your internet (both on the computer you are using and the phone where you have MitID).
If you get a message saying your MitID has already been used to sign, think about whether you might have used your MitID to help another board member.
If you can’t sign because it says that you (as the reporter) haven’t assigned bank accounts, go ahead and assign bank accounts.
If you are using the MitID device with the code viewer, the issue could be that you are using the wrong code. There is one code that forwards the request to the MitID app, and a DIFFERENT code that redirects you to the code viewer. So double-check if you're using the right one. You can read more about using the MitID code viewer here.
If MitID asks you to enter a password AFTER entering your User ID, you should be able to click "Change MitID identification method" and then choose "MitID app" or "MitID code viewer" as you usually use. Not many use this so-called "Password," but most people use either the MitID app or the Code Viewer.