There isn't enough memory to perform this operation. Close unneeded programs and try the operation later.
When I tried to open a certain form (in design view or in form view).
Needless to say, I closed all the programs available (including my messenger) and it didn't help much.
The reason was: too much IIF() in the text boxes of the form. Access had problems loading it.
The solution: Copy the form from the backup.
Move all the IIF required to the back end (in my case: the underlying SQL view).
Now the form loads up quickly and correctly!
Moral of the story: don't use too much IIF().