Projects using GWT 1.5 or lower may only specify one entry point module to compile

Despite

Having the 2.0.3 GWT plugin installed

Never having used the 1.5 GWT plugin

I was getting the following error when clicking the GWT compile button :

 Projects using GWT 1.5 or lower may only specify one entry point module to compile

The solution was to move my GWT dependencies above my Maven dependencies.

Right click on the project -> Build Path -> Configure Build Path... -> Order and Export

Click on GWT SDK and Up until it is just below the JDK.

Please make sure the -vm option in eclipse.ini is pointing to a JDK

Ececutive summary : put the vm argument on the line after "-vm" in eclipse.ini.

I got the following dialog after a fresh Eclipse install :

The Maven Integration requires that Eclipse be running in a JDK, because a number of Maven core plugins are using jars from the JDK.
Please make sure the -vm option in eclipse.ini is pointing to a JDK and verify that Installed JREs are also using JDK installs.

The Installed JREs were already pointing to a JDK. I set my my eclipse.ini to : -vm C:\Sun\SDK\jdk

-vm C:\Sun\SDK\jdk\bin\javaw.exe

No luck.
Eclipsepedia has an eclipse.ini.

I put the vm location on the next line and everything worked.