To use HTML Help over a network when the CHM file is installed on an individual computer, you must register the CHM file in the Windows Registry. This is because current Microsoft security features block HTML Help files viewed from a network drive.
You can use a free tool, HHReg from EC Software, to register each CHM file in the Windows registry:
http://www.ec-software.com/products_hhreg.html
CHM files viewed from local drives are not blocked by these security features.