Int 25 reading sectors of the Hard Disk

simon204

How do I execute an Interupt 25 to read sectors from a hard drive.
I can execute an Int 25 (Absolute Disk Read) on the A or B Drive but NOT the C Drive.
Registers AL, CX, DX, and DS:BX are set to appropriate values but Int 25 returns the error code 0207 in AX.
My DOS manual states this to be -
02 - Bad address mark,
07 - Unknown media type
but this is almost meaningless to me, is a call to another Interupt required for DOS to 'know' the media type.
I've tried my code on two seperate machines, on both I can read the A drive but not the C drive.

Any help would be greatly appreciated
Simon