This is a copy paste from my post in a thread on the General Tekkit SMP board here. I thought it should be here as well/instead. To fix the following error: Error occurred during initialization of VM Could not reserve enough space for object heap Could not create Java virtual machine. Edit(right click > edit) the launch.bat so that it contains the following: java -Xmx1G -Xms512M -jar Tekkit.jar nogui pause You should also think about whether you have enough RAM to be running the server. Some other things that have come up: The server folder name cannot include "!", this probably applies to other special characters as well. If the server complains "too small initial heap" you most likely forgot the M on -Xms512M Some more details. G=Gigabyte M=Megabyte So Xmx specifies the maximum size of the heap. it does not limit the amount of memory tekkit will use, only the heap which is one use for memory. Xmx should be less than total free memory, AND if you are running 32bit java it should be less than 1.5G. If you get stack overflow errors you should increase this value Xms specifies the initial size of the heap, its not that important in this case, ideally keep it around what the server uses right after it starts up, 512M is plenty for me, this should never really need to be changed.