This error can arise for two main reasons:
1. The file is a single line file with no carriage return at the end of the line. A line delimited file (a file where each transaction is on a separate line) that only has a single line must include a carriage return at the end. This is in order to show the system that the line has finished.
To correct this, open up the file in Notepad and at the end of the line press the 'Enter' key to add a carriage return. If you are unsure where this file is located follow the 'Locating and opening the input file' steps in this related article: How do I compare the file format ePay is using against the input file?
2. The input file no longer matches the file format (template used in ePay to read the contacts of the input file). Specifically, the file format is looking for certain text that no longer exists such as a file header.
To compare your file to the file format follow the article: How do I compare the file format ePay is using against the input file?