Hi Pravanjan,
this kind of error, it can be one of two things normally :
Either 1) exhausting memory
or
2) code trying to execute prohibited method in the sandbox. (if the error only happens once in a while, it's most likely not that)
So you can either try to boost your instance type to a bigger one, or check in your code to make sure you don't handle just a bit too much (sometimes dropping the number of processed items in a cron job can make your cron go through).
In any case, this kind of question as to why something doesn't work would be better directed at stack overflow, where we have people (and the community itself) monitor certain Google tags :). Be aware that, to open a question on Stack Overflow, you would need more details than you provided here ( a code snippet of your cron, an explanation on what it's trying to do, etc)
Cheers!
In any case, this kind