Problem/Bug Server 'Out Of Memory'

Hi All, My Bukkit server has been running for 2 weeks straight with a restart every 24 hours. I have just went t o restart my server as usual dead on 21:00pm (United Kingdom time) and this is the log i got when i booted up the server again: http://jpst.it/x0fv
I have never had this problem before but the server keeps producing this same error log with this line being the suspected culprit : 'java.lang.OutOfMemoryError: Java heap space'
I know what most people will say "Buy more RAM" which yes i may consider it but i would still like to know why within the space of 5 minutes it suddenly broke? The rest of my PC including Minecraft works fine however I have people lined up to go on this server and would like to get it back up and running again as soon as possible. Any help would be greatly appreciated!

If it helps at all here is the *.bat file that starts the server :

java -Xmx1024M -jar craftbukkit.jar -o true
PAUSE

Thanks, Jack

P.S. If you need any extra information please ask me for it and whoever can give me a working response will be rewarded on my server should you choose to join it

P.S.EXTRA. Sorry forgot to mention I have one stick of DDR3 RAM installed it is only 4GB and 3.87GB of it is usable.

 

Sorry for posting in the wrong section

 

Try fixing all those other errors first. If that doesn't work, try assigning more RAM.