not udp karst, it means that your ip is unreachable by the vast majority of peers, not just udp, since lowid stems back from the days of edonkey2000 and that didn't even use it
You must ensure that your firewall isn't blocking TCP access to edonkey/emule ports. It can be produced artificially with a dud connection with a server, you should really reconnect to a few servers, if it repeatedly happens then you have a problem, most likely one of the following
a) your packets to the standard emule ports are being lost, ie. running two clients with the same ports from your ip. The data will get lost and you can't communicate with the server or peers
b) your nat/firewall is loosing packets to your emule ports, check your firewall (ie. especially make sure internal firewall is off)
c) your isp is blocking ports to emule. This is serious, and can seriously prevent you from effectively using emule. Try changing ports, but hold little hope of connecting without a series bottleneck.
d) the server is having trouble reaching your ip, through blocking or error. Reconnect or change servers.
UDP does not effect id though, you can safely turn it off and still get a highid. UDP is a protocol that is unsafe, and is merely a broadcast of expendable information.