[Urgent]: [WARNING] CAN'T KEEP UP! DID THE SYSTEM TIME CHANGE, OR IS THE SERVER OVERLOADED?

Now, I know there are many noobs out there asking the same question, but not only am I getting this message, but I am also have severe lag spikes, players losing connection, and freezes.

System info:

Mac OSX Lion 10.8
RAM dedicated to my server: 19 GB
Java 7
Processor: Intel i5 (2.7 GHz)
Server Worlds: 7
Plugins: 28 (Including Essentials and WorldEdit)

Info at first problem:

Players: 10/100
WorldEdit: False
TPS: 20

Nvm, someone took a fortune 1000 pic and get like 100000 items

EDIT by Moderator: merged posts, please use the edit button instead of double posting.