Does this idea suggested by @Joel_McClung help? I'm experiencing exactly the same issue btw (also trying to use the ntp.org pool - but the German one).
It seems to be a common problem on PCT 6248 or more switches from the 6200 series, even on the latest and greatest 126.96.36.199 firmware version.
Happy New Year (even if it's already a few days old) and best regards
EDIT: I'm with Joel - it could be the Round Robin method to randomly choose NTP Servers, but I don't think so anymore after trying to use three German timeservers from different universities. I can also see a
|Failed to Resolve DNS address for Server (null)"|
in the debug log, but those servers are definitely not using Round Robin.
Even if I only specify one address (e.g. times.tubit.tu-berlin.de) it will fail. Does it only accept numeric IPs?