Donning PSI::ESP I would say that it means that something went wrong, and you do not understand the error message. (Possibly it could be better, for instance it could use die and you would have a file and line number to assist you.)

If you have basic Unix utilities available I would go to wherever your sourcecode is and type:

grep 'Reading Header Failed' *
[download]

If you are on a Windows system you will need to use " instead of ', and you will need to have the grep utility installed. You can get it from the PPT project if you don't have it already.

That will not tell you what went wrong, but it will help you find where the error message came from. By trying to understand the source code there, you should be able to puzzle out what was expected for a header and (after some work) why it didn't arrive.