iRule for Response Header "content-length"

Thanks. I am stucked in weird issue. It is for sharepoint 2007 environment. We are migrating from sharepoint 2003 to sharepoint 2007. We have configured an iRule which redirect 404 and file not found requests to the migrated site. The problem is when sharepoint is accessed via UNC. As standard functionality windows check for files like thumbs.db, file/folder present etc. which returns "404" code. This is where the UNC access stops working. Actually the file like thumbs.db etc. are not present on the sharepoint server. We would not like to have a rule which will not redirect if the return code is 404 and "content-length" is not equal to zero.

 

 

I will try your suggestions.