PHP application logged out automatically

[ajaykataria]

Friends,
I am using windows OS and using PHP and mysql over apache ..My application is like that user login into the application fill their data and submit form...After submiting the form they gets automatically logged out??? Why.

PAN India approx 750 users using this application..

Question:-
Is the apache configuration issue?
simultaneous users may affect my application performance??
APAche error log:: Server can not process threads

pls help