Apache2 Permission

I have a little problem!
I have Installed the Atmail E-Mail Server! Everything works!! Thats not the Problem...

I Have Installed the ISPConfig3 Interface here works everything too...

But now i have a other Problem with Apache User...
Normaly you will find this in the Apache2.conf or envvars.conf

But the Atmail - E-mail Server Change this to:

Ok now is in the Apache2.conf - > User atmail -> than the complete Atmail WebInterface works...
but
the ISPCOnfig 3 Interface doenst work anymore .. here i will become following error:

If i change the User back to normal ( User ${APACHE_RUN_USER} ) than the ISPCOnfig3 WebInterface works but the Atmail Server Interface doesnt work anymore ... here i will become a zend error ... that means Apache2 must have the user atmail to work right....

Anyone knows what to do?

Sry for my bad English and explain

 

Can you post the exact Zend error message?