RSS:error

I have a simple blog using WordPress standard themes “The Twenty Twelve Theme”. I dont use a external server with WordPress installed. Just the Online-version of WordPress.

The RSS-feed on my blog has work perfectly for long time but now I got this error:

“RSS-error: This XML document is invalid, likely due to invalid characters. XML error: Invalid character at line 199, column 31”

My problem is that I not can change this XML-problem. How can I delete this blank-row it that is the problem, when I use the online version of WordPress?

Regards PO