I've never had any trouble loading a Matedit matrix. Did you put this code at the top of your program before your main loop?
`declare the MatEdit variables
Dim BigMatrix(600,600,1)
Dim StartLoc_X(1): Dim StartLoc_Z(1):Dim Info(2)
Dim TArrayX(1): Dim TArrayZ(1): Dim FKey(10,1)
Dim ColData(100): Dim ZoneData(100): Dim Tiles(500,500)
Dim OverTexture$(100): Dim OverName$(20): Dim ReplaceTex(100)
Dim MOffsetX(25): Dim MOffsetY(25)
Dim MWire(20): Dim MGhost(20): Dim Lock(20)
Dim MatX#(20): Dim MatY#(20): Dim MatZ#(20)
Dim MatWidth#(20): Dim MatHeight#(20)
Dim TilesX(20): Dim TilesZ(20)
Dim MatHi#(20): Dim MatLo#(20)
You must have that code in your main program file in order to load the matrix. Hope this helps