In case anyone else has this problem, you may be interested to know I have
found a solution. Somehow an old version of mapi32.dll was installed in
windows/sys32 folder (dated 1996). When I installed a newer version from my
MS Office CD the problem was fixed. I found the solution on a Hauppage
website by doing a google search on WNetEnumCachedPasswords.
All's well that ends well!