Hello Pradheep,
It looks like you're not alone in getting that error. Seems it happens a lot, but nobody has a definitive answer. It appears to be intermittent, which is may be why it isn't tracked down yet.
You could try these solutions recommended by Akeeba on their public forum.
www.akeebabackup.com/support/akeeba-back...m-delete-failed.html
I tried tracking it down through the language file to see what it was associated with in the language file, and it doesn't seem to exist in Joomla. It also seems to be tied to a java script.
From my research, it seems that the problem eventually goes away. I'll keep digging and let you know if I come up with anything.
Cheers,
Ed