Not Enough Memory

Hi. My database was chugging along just fine until one day...
It began to tell me "There isn't enough memory to perform this operation.
Close unneeded programs and try the operation again" when I tried to open a
form.
I closed all programs except for Access and the error still popped up. It
only happens to a handful of my twenty or so forms. Any suggestions as to
how I can fix this?

Thanks ever so much!
Stacey