Error msg "Not enough memory to perform operation. Delete some data"

I have this above mentioned mem prob with my n72. when i check my card mem it shows over 100 MB free, wen I check my phone mem it shows 19 MB used (out of total 20MB) some 84KB free only...wen I check the memory details in the file manager, it shows used 19 MB but doesn't shows where and which application is using it, all app like contacts, msg, etc. are using a total of aroung 2MB space den wer is my mem being used?...i have removed all msgs, audio, video and all kind of documents from phone mem, cleared call log, i tried rebooting with and without card...still cant figure out who or where is the 17+ MB phone memory is getting used. Before i reset/format the phone I want to know if some one can help me figure out what is using the phone memory...