Debugging Access/SQL database

We have a bunch of errors all of a sudden coming up in our access front end of a database my company uses. I am looking for someone that can take a look at it with me and figure out what is happening and how we can resolve it.

There are multiple errors:
Runtime Error '2501': The OpenForm action was canceled

The expression on open you entered as the event property setting produced the following error: user-defined type not defined