The UCS server crashes out of sudden and need to be rebooted.
In /var/log/daemon.log you see messages like this:
1:Sep 13 21:20:04 ucs cron: sendmail: warning: fork: Resource temporarily unavailable
Increase the number of allowed processes on your host as follows:
ucr set security/limits/group/Domain Users/hard/nproc=10000" #default 1000
Just keep in mind this raises the limit but does not take care about the root cause. In case the server still crashes after a while with the same error you should check why there are so many processes running.
See RedHat article:
“Raising limits while not fixing the root cause of the process […] leak may lead to worse, unpredictable consequences.”