Service 4WD Message.....

[solarflare]

I started up my H2 today...mind you, it basically sits in the garage and I take it out about every two weeks or so. It has 24K miles 07' Lux model. Started her up....was fine. Let it warm up, and then realized I had to go back into my house. Shut it off, and turned back on....went to go up the road and the Service 4WD message came up on the dash. I turned off the message.
The 2 drove fine...no issues. I called Onstar and they said the 2 was giving a code of 4wd transfer case problem. I stopped and was on dirt and went into 4wd hi lock, with no issues whatsoever.....and then back to regular 4 hi. It ran fine the rest of the day....no issues.
I'm just curious if this is a common issue from sitting too much or if there is something that needs to go in for service immediately??? Any advice would be great!