Here's an extract from one of the sites I visited in looking for an explanation of your problem:
"Firstly, I will mention that ACM stands for "Audio Compression Manager". This is the library written by Microsoft as part of Windows which acts as the programmer's interface to the codecs.
The ACM really belongs in MMSystem.pas (which handles Windows multimedia) but, for some reason, it has been omitted. The first task therefore is to find a copy of MSACM.pas, which is an API conversion of this API. The one I found most useful was the conversion by Francois Piette, which was posted on Project Jedi (
www.Delphi-Jedi.org). "
Seems to me that you are missing some essential software to open the files but without knowing the incoming file format I cannot advise on any alternative. Have you contacted the sender(s) of the file(s) ?
Perhaps a more knowledgeable forum member will pick up this thread.