First of all, I think you have a file or folder with an invalid charater for Netware 3 to recognize. To pin point this, copy the contents Folder by Folder until you get the error. This way, you are at least able to find out which folder the file with an invalid character is located in.
Secondly, I am sure your slow transfer rate is caused by physical problems. Make sure your cables, if CAT5, that they are properly terminated with the A or B standard on both ends and make sure the cable is certified. Make sure your cable run does not exceed the standard and there are no loops, kinks or tight bends with the cable. Finally check for obvious interference emitting devices near the cable.