When we click on the "insert database field" icon in Report Builder, we see a red X next to the field name. The following error is also generated: 

java.lang.NoClassDefFoundError 

at java.lang.Class.forName0(Native Method) 

at java.lang.Class.forName(Unknown Source) 

at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(Unknown Source) 

at java.awt.image.BufferedImage.createGraphics(Unknown Source)

Edit your /stoneware/bin/webNetwork.lax file and find the line: 
lax.nl.java.option.additional= 

Add the following to the end of the line : 
-Djava.awt.headless=true 

Save it, shut down webnetwork and restart it and the problem should go away.