This could be one of two things:
1. If the function is unknown, you may not have the #Include file at the start of your program.
2. The tutorial you are following uses an older version of Matedit than the one you are using. Check the docs with the version of MatEdit you are using to see that you are using the call correctly.
Your version may use the format:
Success=LoadMatrixPro("matrixname",1)
(The Pro version is a different include file to the DBC version).
TDK_Man
For MatEdit Pro Progress Reports, see the MatEdit page at
http://www.matedit.com