I was wondering which ppmd method you use, i saw that there is ppmd_a,ppmd_b trough n
The Chilkat Compression class (not the Zip, but the Compression class) implements PPMD variant J. This is the PPMD compression used when the Compression.Algorithm property is set to "ppmd".
The Chilkat Zip class can decrypt ZipX archives where the compression is PPMD. However, this variant is "I" and not "J". Unfortunately, the "J" variant at this time is not viable on 64-bit machines. It is actually available on Linux, but only for 32-bit machines.
Unfortunately, this is not something that can be resolved. If anything, the only solution for the more distant future is to bring variant J as an additional algorithm for the Compression class, which would then be viable on both 32-bit and 64-bit, across all operating systems.