error 406 Not Acceptable

Hello,
on a new instalation without any tweaking of your code i get this type of error, when I try to update users profile.

URL: http://www.dmediabulgaria.com/projectpier/index.php?c=account&a=edit_profile&active_projec...
"
Not Acceptable
An appropriate representation of the requested resource /projectpier/index.php could not be found on this server.

Apache/1.3.39 Server at dmediabulgaria.com Port 80
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I can give ftp details to the developers to investigate the problem. Please can you help me.