In the HexEdit 5.0 beta (build 1349) I get the following message when trying to view any of the help:
Navigation to the webpage was canceled
What you can try:
Retype the address.
BTW, Andrew - it is nice to see that you are active with HexEdit again.
I tried it and think I know what the problem is, though when I try it I get different results -all I get is blank help pages. Because the help file is just extracted from a downloaded zip file and not installed with a proper installer it is marked as blocked. (Note that I am working on creating the final version of HexEdit 5.0 with a proper installer to be released in a few weeks.)
To fix this just find the help file (HexEdit.CHM), right-click and select Properties. Then in the 1st (General) page click the "Unblock" button in the bottom right corner and click OK. That fixed the problem for me but get back to me if this does not fix it. (You might also try unblocking .exe and .dll files too.)
Unblocking the .CHM file fixed the broken help.