It is tricky to fully answer your question given the information you have provided, however, some initial thoughts:

Are you using purely quota based archiving or age & quota?

Can you list out your policy settings?

What size mailboxes do you have in Exchange, and what quotas do you have set?

Do you create shortcuts?  What is the content of those shortcuts?  Depending on how much information is left in the shortcut, it will of course take more space up in Exchange.

Hi Rob

thanks for your reply, I think you are right once it crosses the send/receive quota, archiving won't work.

Yes we are using both age & Quota base 

we have different Quota limits for users like some have 100mb limits & some have 200 mb,

In quota based policy when 30% of total space is remaing it will start archiving.

we have increased the archiving tasks  time window to see if it will help us to solve the issue.

Perhaps if you have a few mailboxes to target, you can just do a 'Run Now' and select 1-2 of those?

HI

Kindly follow the mentioned links, you will get a proper knowledge of Exchange database Arhiving.

http://technet.microsoft.com/en-us/library/dd979795.aspx

http://www.howexchangeworks.com/2010/03/setting-archive-mailbox-quota-in.html

Was this resolved in the end?