Web User Control works fine in dev, but only briefly live

[lithoman]

I've created a Control that builds a gallery, and it's working fine in
my development environment, but keeps breaking live. The funny thing
is, all I need to do to fix it is change the class name in the Control
directive at the top of the file (which as far as I can tell is
inconsequential as long as it is distinct in the app) and it works
again, for a few hours.

I have other controls that are doing fine.

Any ideas on what to look at?