Could be a number of things.

Firstly, make sure that no other users are in the database while you are
changing the forms (and that you don't have multiple copies open.)

Does the form have a subform? If so, make sure you have a text box on the
subform for the field named in the subform control's LinkChildFields
property. You can set the Visible property of the text box to No, but it
must be present in Access 2002 and 2003 to prevent a crash that appears to
be related to the AccessField type.

If that does not solve the problem, a decompile might. Try this sequence:

1. Uncheck the boxes under:
   Tools | Options | General | Name AutoCorrect
Explanation of why:
   http://allenbrowne.com/bug-03.html

2. Compact the database to get rid of this junk:
   Tools | Database Utilities | Compact

3. Close Access. Make a backup copy of the file. Decompile the database by
entering something like this at the command prompt while Access is not
running. It is all one line, and include the quotes:
   "c:\Program Files\Microsoft office\office\msaccess.exe" /decompile
       "c:\MyPath\MyDatabase.mdb"

4. Open Access, and compact again.

5. Open a code window.
Choose References from the Tools menu.
Uncheck any references you do not need.
For a list of the ones you typically need in your version of Access, see:
   http://allenbrowne.com/ser-38.html

6. Still in the code window, choose Compile from the Debug menu.
Fix any errors, and repeat until it compiles okay.

At this point, you should have a database where the name-autocorrect errors
are gone, the indexes are repaired, inconsistencies between the text- and
compiled-versions of the code are fixed, and reference ambiguities are
resolved.

If it is still a problem, the next step would be to get Access to rebuild
the database for you. Follow the steps for the first symptom in this
article:
   Recovering from Corruption
at:
   http://allenbrowne.com/ser-47.html