Forms authentication failed for the request. Reason: The ticket supplied was invalid.

HI , 
I have a webapplication hosted on server using form authentication , and this is not web farm there single server is involved and i am accessing this on a client machine and even tried accessing it on server it self, 
i am able to login in site but after few clicks i am redirected to login page and in event viewer this
Event code: 4005 Event message: Forms authentication failed for the request. Reason: The ticket supplied was invalid. Event time: 1/13/2015 11:54:26 PM Event time (UTC): 1/13/2015 6:24:26 PM Event ID: 8f2f3f795d504a6f8b48d6087d8dbd4f Event sequence: 2 Event occurrence: 1 Event detail code: 50201
i tried re-setting cookie name 
I changed machine key generation and un checked Autogeneratiion of keys
but nothing seems to work , it keep on expiring
 Please help as soon as possible..

thanks in advance...
Dheeraj kumar