Trouble with Solo Groove

[Slackerprince]

I've really been enjoying the advice and experiences of those on this particular forum!
So, I'm a fairly new bassist with a background in guitar, and my situation is this: That I can jam with others or jam with CD's pretty good, do some cool scale runs and get some groove going, but just sitting with the bass and the amp, I seem so directionless and all my attempts at starting a cool bassline seem so random and crappy. When I have jammed with other people, I kind of need the guitar player to get something going so I can fumble around, find the key, then start a groove. I have a good ear and can hear the music and cruise along, but can't seem to get something going that sounds decent without any other accompaniment.
Why is that?
I appreciate any help and suggestions.
Thanks.

S.

[gr8fulhiker]

Start simple - dead simple. Prime the groove pump by laying down a simple groove that you can build on. Play with only index fingers to force yourself to keep it simple at first and play it longer than you want to. This will lock your brain into the groove and keep you locked in when your notes drift away from the original line as you add flavor. Keep the genie in the bottle and build slowly. When you're by yourself you have to lay down your own foundation.