Have you tried uninstalling Play Store & then reinstalling.
Also pls. convey which ROM you are using. as some custom ROMs come with their Gapps package.
Yes i have tried uninstalling play store and reinstalling it but it did not work, i am using stock ics 4.0.4 with speedmod kernel.
But the good news is that i can now download from google play
This is what i did:-
After trying everything with no positive result i flash stock ics 4.0.3. again but this time with clear cache, data and delvic wipe via mobile odin. I tested it and it did not work, infact my keyboard got messed up, whenevr i try to write it reflected as "null" for every letter i typed. So finally i had no option

then i thought of restoring my fone with the nandroid back up i did just after flashing my 4.0.3 ICS ROM and SPEEDMOD K3-10 kernel(it was a back up b4 i started flashing different ROM now n then ) . I did and walla its back to normal

now i can download from google play.
The real problem was not on google play data but in my download manager, it was mess up after i continuously flash ROM one after another. I couldn't even download some files thru the browser during that time. Now its back to normal. Thanks to my nandroid back up. Its always safer to do a nandroid backup b4 things are messed up.cheers
Sent from my GT-N7000 using xda app-developers app