DET,
It is possible that the silicone in the back, I assume behind cork bark or something similar, could still be slowly curing or that the acetic acid from the curing process is slowly releasing through your background.
Here is a similar thread:
http://www.dendroboard.com/phpBB2/viewtopic.php?t=5909
If you are using the standard backgrounds (coco panel, cork board, tree fern panel, etc) then you effectively have a giant sponge on the back of your vivarium that can retain some of the smell for a while.
In general, put the aquarium in a warm area to expedite curing, put a fan on it to recirculate the air and get the acetic acid (which is probably what you are smelling) out of the enclosure. Fortunately, the gases are non-toxic (unless you used a ton of silicone and don't have a reasonable amount of air exchnage) and it is likely that whatever acetic acid is off-gassing is not very strong.
If you have the time, it probably wouldn't hurt to air it out with a fan or something and try to dry the enclosure out as much as possible. But, unless you used an abnormal amount of silicone and are going to put in the frogs tomorrow you probably won't have an issue.
Marcos
