The 31-year-old joined Palace from the Shrimpers last summer but made only five league starts and was eventually loaned out to Leyton Orient.
"I'm delighted to be down here," he said. "It was frustrating last year but I've got fire in my belly and I'm raring to go.
"The move came out of the blue really. There were a couple of other clubs interested and (Palace boss) Dougie Freedman didn't really want me to go.
"But I want to be playing regular first-team football and when Lee came and approached me this was the only place I wanted to go."