OS Commerce error Rectification in Windows Server

Hello Guys, Need a small error to be rectified in a OS Commerce website that is hosted in Windows Server. When all the products are added and when the Paypal payment gateway is selected its going smoothly. But when the payment is selected as COD, it shows 500 Internal Server Error. The error could be due to file permission or some small change in the server. So need person who have already rectified this error or experienced in handling OS Commerce in a Windows Platform Few more changes are in the texts only which won't take more than one hour to do it. The total cost for this project can't be more than 20US$. Interested bidders will be given the URL to have a look into it. Good Luck!