run_av (ClamAV-clamd) and ClamAV-clamd av-scanner FAILED - unexpected

I get a strange error when scanning email.

Sep 17 15:13:26 mail amavis[616]: (00616-02) (!)run_av (ClamAV-clamd) FAILED - unexpected , output="/var/lib/amavis/tmp/amavis-20140917T141903-00616-Vqttx7KO/parts: lstat() failed: Permission denied. ERRORn"
Sep 17 15:13:26 mail amavis[616]: (00616-02) (!)ClamAV-clamd av-scanner FAILED: CODE(0xf8fde0) unexpected , output="/var/lib/amavis/tmp/amavis-20140917T141903-00616-Vqttx7KO/parts: lstat() failed: Permission denied. ERRORn" at (eval 113) line 899.
Sep 17 15:13:26 mail amavis[616]: (00616-02) (!)WARN: all primary virus scanners failed, considering backups

I added amavis to clamav group and vice versa but I think its not the trick.
can somebody help?

please comment so I add necessary infos.