What it comes down to Sue, is that when one sings solo, there is a lot of room outside of time signatures, key, timing, etc for interpretation. When all I am worried about is myself, and I don't have to be concerned with any sound except what I put out, I can be very interpretive.

When I am playing with a band, or jambing with others, I have to be concerned about consistency of time, chord voicings and progressions, total sound of arrangement. I can still be interpretive, but only insofar as I stay within the friendly walls of the arrangement, so I don't throw off the other performers, hence mucking up the sound of the arrangement.

Once one has played with a given set of performers for a goodly amount of time, then they become used to your peculiarities of style and can move with you, restoring a bit of your ability to be innovative.

Judging from what I have read of your style, it is my guess you are an interpretive singer. I would guess it will take you a bit to get used to a band, but it can be done. But practicing singing with a metronome, and staying within that time and tempo would go a long way towards preparing you for singing with others.

Mick