As them what VERSION of EP their file is structured for...

1.2.5.4 and 1.2.5.5 use a TAB DELIMITED TXT FILE FORMAT

Later versions use CSV DELIMITED FILE FORMAT

... Then there is the EP Advanced (Version 3) which is commercially available - it uses TAB FORMAT too.

Open your supplier's file in a plain text editor (such as notepad++ or Emerald Editor)...

... are the fields separated by a TAB... or a COMMA ?