Ok, 
I got a reply on forums.cpanel.net.     
-----The cPanel error log should let you know the reason for this failure. Could you check to see if there are any specific error messages listed in /usr/local/cpanel/logs/error_log when you encounter this problem?   
In most cases, this is the result of the cPanel process not having enough memory. In "WHM >> Server Configuration >> Tweak Settings", under the "System" tab, could you try increasing the following value:   
"Max cPanel process memory"-----   
I am not sure if the second option it offers will work, 
if not, 
maybe you will have to check the log, 
and I'll post it on again.     
http://forums.cpanel.net/f5/cant-fetch-per...les-209532.html   
Oh, 
By the way, 
this topic can be merge with http://www.helionet.org/index/index.php?showtopic=9308   
Thanks!