back up fail due to "locked by dependencies"

When I'm trying to backup my course (large course) in Moodle 2.0.7 in the " Confirmation and review " part of the backup there are red crosses and a lock which says "locked by dependencies" also one unresponsive script Warning is come regarding ??

After that I stop above unresponsive script which come  pop up . moodle asking for“You must enter a valid filename for this backup”

I didn’t understand how to solve this problem ???

My moodle setup is is install on linux system which having following configuration.
Apache version                 >> 2.2.23
PHP version        >> 5.3.20
MySQL version >>5.5.28-cll

Thank you for the help in advance.