Same Application On The Same IIS Logs User Out

Hi,
I have identically same applications on the same IIS.
But when I login one, the other logs me out by IIS.
Event Viewer logs this error:
Event code: 4005
Event message: Forms authentication failed for the request. Reason: The ticket supplied was invalid.
Event time: 07.09.2010 17:00:51
Event time (UTC): 07.09.2010 14:00:51
Event ID: a87e86a77ab641a99dcb2904765eb658
Event sequence: 24
Event occurrence: 21
Event detail code: 50201
 
Application information:
    Application domain: /LM/W3SVC/1/ROOT/ECZKariyer-5-129283414711424580
    Trust level: Full
    Application Virtual Path: /ECZKariyer
    Application Path: C:\inetpub\wwwroot\ECZKariyer\
    Machine name: BIZALPERE
 
Process information:
    Process ID: 2040
    Process name ...