If root ("Administrator") access is available, please check the cPanel error_log for logged message detail that may help pinpoint the issue. The following command may be used via root SSH access to monitor the cPanel error_log for new output while attempting to reproduce the issue:
Originally Posted by ST1
# tail -fvn0 /usr/local/cpanel/logs/error_log
The above is correct and disk usage is important to check; if the account disk usage has reached the defined disk quota (limit of disk usage) then this may be the cause as the file system would not allow new data to be written beyond the defined quota. The current status of disk usage is displayed on the home page of cPanel (the same page that is displayed after logging-in).
Originally Posted by saninfosys.com