[imp] Undefined index: msgl

[sasha123@libero.it]

Hello, 
I have installed imp3.1, seems to work all, but when I try to read a message I have the following error: 
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Warning: Undefined index: msgl in D:\InetPub\wwwroot\cgi-bin\php\horde\imp\message.php on line 178
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where mistake? 
Thanks

Best Regards
Sasha