Hellou.
Ive been working with osCommerce for more then 10 years.
If you can provide the error its possible to lower the price.
For now all i can say, is that during all those years ive been slicing projects into html/php osCommerce code, and doing all sort of mods and supporting them. If you need further advice or help with developing your own mods, we can cooperate on lowered stakes.
If my proposal is attractive to you please let me know.
If not, just tell me how i could improve myself in the future :)
Best regards,
Trygon eXtreme