cron::i can't run cron untill i delete all feeds

already happen many times :
if i don't delete some feeds , sometimes i have to delete all , then run cron , then add the feed again……

the cron fail :

Fatal error: Maximum execution time of 240 seconds exceeded in C:\root\feed\includes\common.inc on line 501

Fatal error: Maximum execution time of 240 seconds exceeded in C:\root\feed\includes\session.inc on line 56

Fatal error: Maximum execution time of 240 seconds exceeded in C:\root\feed\sites\all\modules\memcache\memcache_admin\memcache_admin.module on line 224

Fatal error: Maximum execution time of 240 seconds exceeded in C:\root\feed\includes\session.inc on line 14

though i don't think that it must duil to this module ,i suspect.