Need help with a progress bar

I don't understand this error…

code:

http://pastebin.com/ea9LncrA

eg. I type cAPI.percent(1,60). then it says:[string "cAPI"]: 93: attempt to compare nil with number

but if I type cAPI.percent(5,11) or cAPI.percent(7,10) , … then it works fine

look at this program: http://pastebin.com/HmZbq89u it uses this function and it works.

:huh:/> :huh:/> :huh:/> :huh:/> :huh:/> :huh:/> :huh:/>

Ok found the mistake… just added if pb == nil then pb = 0 end at line 90 and all works fine now.