Massive hugs. I felt this way when DD1 reverted back to wetting her pants 12 months after being TT.

I guess I would be thinking about whether the problem was psychological or physical.

If it is psychological then I would imagaine that positive praise would be a good approach. Maybe even start up a rewards chart.

But yet again the issue could be physical like my friend found out with her son, who has a problem with the muscles in the anus.

Sorry I wasn't much help...