I was browsing all the posts in this forum and I found this. I know the post is old and the answer obvious, but still people might get confused as the information available here is scarce and spread all over - so I will just answer this for people who find the question via search in the future.
You need to include the rate you want to increase by after the command, and the command must be in the correct module.
For example, to increase the exp rate by 15 times you would:
- Open the Server Patch Config program that you start the services from
- Expand GameGroups
- Expand GameGroups01
- Right click on Game and select Command (Service must be running >)
- On the command line in the new window enter:
/exp2xenable 15
- Look for the result in the log portion at the top of the window
I hope that clears it up.