[Serusers] xlite registration error 500 : Server Internal error

hey all , my problem is a bit strange . i have succeeded in compiling ser 0.9.7 on solaris 10 x86 arch and the compilation process went smoothly without any troubles ( i mean the last time i compiled ser ) after that i have configured Ser to work with MySQL 5 and aslo there werent any problems happened the problem is : i have added some users in the subscriber table to check that ser is preconfigured correctly using x-lite softphone and also there weren't any problems for the first time i registered with xlite , the problem appears when i unregistered the account and leave SER running for several hours without any user'registration ( about 10 hrs SER is idle or more ) So my question is : is there any pre-determined period that ser shouldnt be idle ? or it there any configuration responsible for determining the max time that SER can rest in idle status ? the error message that appears in the x-lite winow is " Registration error 500 : Server internal Error " Note : when i do restarting SER all things are fine and i can be able to registration without any error , the error appear when i do unregistration and SER is idle thanks in advance