hmmm afaik this error may be thrown if the paths aren't correct. You didn't write the commands under quotation marks or (this would be wrong) ?

P.S.: you should really update Acknex to 7.77 because the wrapper is built towards 7.77

get the C# wrapper:
for A7.85.4 and A8.30.4, Version 2.3.9
at http://acknexwrapper2.matthias-auer.net/ or visit the thread