To obtain the last error that occured then use the LastError function.
Possible return values:
0 - No error.
-1006 - Could not create file.
-1007 - Destination file allready exists.
-2006 - File is not a valid AppleSingle or AppleDouble file.
-2007 - Incorrect AppleSingle version.
-2008 - Could not finalize.
Other non zero values are possible, their meaning will come from the operating system.
AppleSingleDecoderStream Class