Issues with FMP 15 and 360Works plastic 2

[MEgbert]

We are currently using 360Works Plastic 2 with FMP 15 and have done so successfully for some time now. There are two iMACs that are curently not able to run credit cards and are getting a "no content in header" error every time they try to run credit cards. I have checked to make sure the most recent version of FMP 15 is on the computer and any updates to Plastic 2. I have been in contact with our merchant provider and they keep telling me the API is missing but the API is there and other computers on the server can charge credit cards. Any suggestions?

I have also removed the OS and FMP and reloaded with no success.