Homebrew PCBs

i'm sure it isn't the laquer.
also the metaloxide paints should isolate.
maybe there are some "metallic" look paints which conduct but....

it is not very wise anyways to cover up the pcb before you tested it.
i never spray mine at all and if not touched with your fingers they won't 
oxidize too much at room conditions.

you should never assume any circuit working on the first try.
you can only assemble a board fully and spray it without testing when you 
have already made a second working one before.

but take the laquer of for your convenience when soldering to repair it.
take any solvent and brush. if you have plastic parts (connectors etc) on 
the component side don't wet them with solvent.
it may dissolve them.

then get the scematic and test every function.
assuming you have no scope this makes it necessary to get all "nice and 
slow".

fast rs232 voltages you can't test with your meter.

if you provide the scematic somewhere maybe one may have a look on it and 
tell you what even if this is mostly a pcb hardware
manufacturing not debug board....

hope you get it right....

stefan