[imp] Receiving error: "Undefined index: _wp_debugger"

[Aaron Taylor]

Hi,

I apologize if this is a noob question but I searched the archives and  
FAQ before posting and was unable to find an answer that I could  
understand.

I am receiving an error when using imp. When viewing the contents of a  
mail folder it displays under the line "Delete | Undelete |  
Forward..." and above the list of messages. The error is:

Notice: Undefined index: _wp_debugger in /my/path/to/horde/imp/lib/ 
MIME/Headers.php on line 1

I am running IMP 4.1.3, Horde 3.1.3, Apache 2.2.3 and PHP 5.2.0-8 on a  
Debian Linux system. I'm pretty sure the error is related to something  
I've configured in Horde or IMP since another IMP installation on the  
same server but in another VHost runs without the error message which  
probably eliminates my configuration of PHP and Apache. This message  
has appeared within the last three months but I'm not sure of the  
exact date.

Does anyone know what is causing this or can someone point me in the  
direction of the appropriate documentation to find the answer to the  
problem?

Thanks,
      -Aaron Taylor