Hey its a simple problem Try this...
First Go to messaging then go to Settings.... then in Settings... Textmessage ... Select Save messages.... 999 Or Wat ever maximum number it allows...
then in same settings .. "Other"
Then Message memory Select ... Card memory...
Hey if you have taken any songs Or etc. via bluetooth then this problem may occur...
2.If you have any Software... Like SELEQ or FILEMAN...Or Fexplorer Then you can eaisly tranfer the files From phone memory to card and it is advantageous....
Then just go to phone memory then system then Mail then open each file Copy it From there and paste in card memory....
Then file Pasted in card memory just delete From Messaging..
You will not lose your any data
Hope u will get succcessssssss...