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You may have memory issues of corrupted db.

I have run compact and repair but that did not fix it. I will keep plugging away.

Standard text field is 225 for size, does the 225 add up to a max per table number? I know there is a max number of fields per table.

You could make a new table and append the fields into it one at a time until you find which one causes the error. That may help.

How many fields do you have in the table you are trying to add to?

If you create a new table save it and close it.  Then can you get back in and add new fields?

Also are you just adding a field to a table normally/manually? Or is this some kind of append/table query?

Adam,
Just trying to add a field manually, I added several fields and saved as I went then I hit this issue after a few fields were added.

Scott,
I have 240 fields in the table.

Out of curiosity what is the theme of the table? i haven't gotten close to table cap before. It may be worth exploring splitting it up into relational tables if possible. Although that doesnt solve why you can't use the 15 fields you should have left. You went through all the fields and made sure text was less then 255 too you said?

This table has part numbers, serial numbers, and other data specific to an assembly. I agree it will need splitting up down the road but it  will be a while to get to that project.

No I have not reduced all the fields below 255, I have done that to several of them but it doesn't seem to solve the issue.

There are other considerations aside from just the number of fields. See Specifications. For example, your table and field names need to be less than 64 characters, you can only have 10 indexes per table. Things like that. However, if you've got 240 fields in that table you DEFINITELY want to break it up, at least into two tables with a one-to-one join between them. That's a LOT of fields.

Curious... if you import that table into a blank NEW database file, do you still have the same problem?

So I did a couple of tests.
1. I back a copy of the database, and then when to the table with the issue and deleted about 10 fields to reduce the table size.
2. Then I tried to add some more fields and got the same error.
3. Then compacted the database and tried again and received the same error.
4. I created a new blank database and imported the table into the blank system.
5. I was able to add as many fields that I wanted with no issue.

So there is some type of issue with that table.

What is the best process to replace that table with the new one? Does a simple copy and past work?

You could try to copy and paste, although you might copy the error. Try copying just the STRUCTURE of the table and see if you still have the same problem. You can always copy the records over with an append query. You can also try a make-table query. So many different things you could do. :)

Thanks to everyone in this thread that helped on this issue!!!