isolated storage quota increase problem in WP7

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Mobile

Hye everyone,

i m working on Windows Phone 7, and while i m adding data in the app,
i need to increase the memory.

So, i used IsolatedStorage.IncreaseQuotaTo(neededSpace);

where neededSpace is a long variable and neededSpace = 1024 * 1024 * 5;

Also i m using the SilverlightPhone Database.
http://dotnetspeak.com/index.php/2011/02/
quick-start-guide-for-windows-phone-7-database/

when i try to increase the size of the isolated storage, it gives an exception- System.Exception
which says-
"An error occured while accessing IsolatedStorage".

Can anyone say why is it happening.
Thanks in advance.