Trial version of id - all the Preferences are grayed out - I can't change the default from picas inches.
Can you post a screenshot?
Do try cleaning your cache and preferences Troubleshooting 101: Replace, or "trash" your InDesign preferences [2009 Outdated & Locked]
Did you try resetting the preferences? Feel free to report if you need further assistance.
The trial version is full version—it's just time limited.
You can also change the unit of measure by right-clicking a ruler.
Retrieving data ...