Issue on the produced feed with dlvrit

Hi,

I'm using this module to produce feeds from my multiple websites, and I set autopublishing on social networks with dlvrit.
For one of my feeds, I get this error:

line 1, position 3: element declaration should start with '<

But the feed code is the same as others I produce and work in dlvrit..
So what's about this error ? Actually I'm not sure about which part of code do I check.

Thanks