I ran into a somewhat similar problem about two years ago. I was hired to be the "full time" bassist for a local band that had had some moderate success. Mostly low paying local gigs, but some choice gigs out of town - rooms, food, booze, party favors

, and good pay ($200-300/night).
What I failed to realize is that they had a revolving door of bassists since the original bassist left. They had a "go-to" guy, but he would often bail for more high profile gigs and leave them to find a sub. I was under the impression that this guy was out of the picture, as the band leader told me that they wanted someone full time and that I had all of the gigs on the calendar for the foreseeable future.
So I bust my ass and try to learn all of the tunes - they had a ton. I had to transcribe most of the chord charts during rehearsals. We get to my first gigs, and I'm still using charts because there are so many songs and just not enough time to get them all down, but I had a good feel for most of the stuff. The problem comes when the band leader doesn't want to write down set lists. He gets the idea in his head that he's some sort of conductor - dude you're in a jam band, not Count Basie's orchestra

- and he wants to call everything out on the spot. He would call out a song and then start immediately, so that if it was a song that I still needed a chart for, I'd be scrambling through my charts to get to it.
The first gig I got through O.K., because the tunes were simple and I didn't need the charts too much. The second gig went O.K. as far as I was concerned, but after that he said he wanted to use someone else for the next gig. He said my tone was bad, my time was bad, and that I didn't have the tunes down well enough. He said he had a "reputation to uphold" and insinuated that my playing was so bad that it would put the band's future in jeopardy. Well, I had some friends, including fellow bassists, in the house that night and they said my tone was great and the band sounded good.
What it all came down to was the fact that the drummer was pissed at the "go-to" bassist because they were friends. He wanted the "go-to" guy back in the band, but he was too busy going off and playing the higher profile gigs.
Because the band leader told me he was using someone else for the upcoming gig,
I fired myself. I had a bunch of people coming to the upcoming gig - friends, coworkers, etc. Extremely embarrassing. He handled it poorly. If I had known they were just giving me a go to see how it worked out for the first couple of gigs, that would have been fine. But he had led me to believe that I was the bass player. Period. No subs. I could have continued with the band, but I wasn't about to let him boot me off of a gig any time because he felt that I wasn't up to snuff.