Ssrs 2010 informational message

SSAS and SSRS
1

In an SSRS 2010 report that I converted from ssrs 2008 report two weeks ago, I am currently getting the following informational message 42 times:
"Message 14 Could not find schema information for the element 'http://schemas.microsoft.com/SQLServer/reporting/reportdesigner:UserDefined'. D:\TEST\StLetter.rdl 129 12 alReports".

This message did not occur when the report was first converted by now I am getting this warning message today.

Thus can you tell me the following:

  1. What can I do to solve the problem?
  2. On the linformational message line, what does the 129 and 12 stand for? I know the alReports is the solution name. If the numbers 129 and 12 represent line number and position number on the line, would you tell me how to look to see how to determine where these numbers are located at?