Your form may have exceeded the 755 controls allowed in its lifetime. More
likely though it is corrupted. Create a new form, copy and paste everything
from the old one. Then delete the old one. I would then do the following :

First, always work on a copy of the database. Working on the original may
make it impossible for a repair service to fix it.

Download a copy of JetComp.exe:

http://support.microsoft.com/default.aspx?scid=kb;EN-US;273956

Try backing up your forms as text with the undocumented SaveAsText
LoadFromText functions:

http://www.datastrat.com/Code/DocDatabase.txt

Also have a look at the Microsoft KB article:

http://support.microsoft.com/default.aspx?scid=kb;EN-US;209137

Then have a look at Tony Toews' Access Corruption FAQ at:

http://www.granite.ab.ca/access/corruptmdbs.htm

for some suggestions. Unfortunately, some corruption cannot be fixed - you
may need to create a new database, import what can be salvaged, and recreate
the rest.

Although it's a paid service, Peter Miller does an outstanding job of saving
corrupt databases. Try this URL:

http://www.pksolutions.com

I'm thinking that the database is corrupt.

At times like this, nothing beats a good backup.  In fact make a complete
backup of your database now and put it away for safe keeping.

Tony Toews has an excellent web page on database corruption.
http://www.granite.ab.ca/access/corruptmdbs.htm

Allen Brown also has excellent info on corruption.
http://allenbrowne.com/ser-47.html

I have a white paper in a Word document named Fix Corrupt Access Database
towards the bottom this page:
http://www.rogersaccesslibrary.com/OtherLibraries.asp

James,   Are you able to edit/change/delete any of the current controls you
have on the form?

Have you copied the form to another name and experimented with the other copy?

Thanks for the replies, guys.  Turns out the database was corrupt.  I made a
new copy from my backup and all is fine.

Thanks again.

James