I am haiving problems with my Tekkit server also, same problem, but I have no idea how to check how much allocated my server is using. (Dont know how to check)
System spec-
AMD Phenom II x4 965 Processor (3.40Ghz)
8Gb RAM
64-Bit vista
255gb HDD
Nvidia Getforce HDCP GTX 295 (1792Mb)
I have been told multiple times that my PC should run a minecraft server with ease/effortlessly.
I have been running my server for about 2months give or take a few days, the "Warning" message has come up a couple of times but didn't spam until last night. I only have myself, a few friends and a few members of family on on server, max at one time was 13. (Inc me) I have been using the "launch.bat" that i got with the tekkit server download from the yogscast download site and that has been ok untill now, if anyone can help me, would be greatly appreciated. :P