Sounds like you've been sent a file where the sender has checked some additional references. You'll need to check that reference too. Do this...
1. If you haven't already done so, save the attachment to a folder on your hard drive.
2. Launch Access, and open the attachment using File | Open. You'll proboably get the message. Click OK but LEAVE ACCESS OPEN.
3. Now go to the File menu in Access and you'll see the problem file at the top of the list. This time it'll open without launching any forms.
4. Click the Modules tab, open any module and select Tools | References. Scroll through the list -- near the top you will see at least one with MISSING next to it.
5. Note the name of this library. Uncheck the missing reference, scroll down the list, find the library and click the checkbox. Click OK to close the dialog.
Now you should be able to close Access and re-open the file without problems.