Hi Mike,
Welcome to Microsoft Community Forums.
Based on the description, it appears that you are getting an error message "Error DBFNTX/1001 Open error: filename.dbf (DOS Error 5)". I will definitely help you in fixing this issue.
To guide you in the right direction, I need more information from the computer by answering the following questions:
1) What is the name of the DOS program?
2) What is the name of the hotfix?
3) Do you have Windows 7 installed on other computers as well?
4) Have you made any changes on the computer prior to this issue?
Your reply is very important for us to ensure a proper resolution. Please get back to us with the above information in order to assist you accordingly.