VBscript FormatPercent Overflow 800a0006

I have several websites running on a 2003 IIS6 box, all
running basically the same code (each site has its own home directory
and copy of the code). All are running in the same App Pool.

One site gives the 800a0006 error on a formatpercent, another site (on
the same server) does not.

Here's the kicker...the one site only fails if the number is LESS THAN
1.

formatpercent(0.999) ---overflow
formatpercent(1.000) ---100%

The one "abnormality" is that the default script language is set to
jscript, and I call the function via a call to a vbscript block -- but
this works on several other sites on this same server.