Three steps will fix this:
1.) Make sure the HCadMainBase-r.arx is the proper version for this version of CAD-R.
Open windows explorer and browse to "C:\H40\PROG\CAD-R\ACAD2018-64" or "C:\H40\PROG\CAD-R\ACAD2019-64" or whatever version of autocad you are trying to open.
Find the file "HCadMainBase-R.arx". Right Click on it and go to Properties.
Go to the "Details" tab. It will tell you the version. The versions should be as follows:
ACAD 2017-64 ----> 54.1.64.1
ACAD 2017-64 ----> 55.1.64.1
ACAD 2019-64 or ACAD2020-64 ----> 56.1.64.1
For Example:
To get the proper version, re-run the Hydracad-R Install.
2.) Make sure that HydexVB64.dll is in the windows/system32 folder.
Obtain the Lock Fix file from HydraCad, inc. and run it on your machine.
3.) Make sure your support file seach path is correct.
Open up HCAD-R.
Right click on the command line.
Select "Options".
Select the far left tab: "Files".
Click the plus sign beside "Support File Search Path"
There are 3 things to look for in this list:
a.) Make sure the ACADxxxx-64 in there is for the version of Autocad you are currently on.
b.) Make sure there are NO other ACADxxxx-64 for different versions in there.
c.) Make sure that all entries which start with "C:\H40" appear BEFORE entries beginning with "C:\HES" in this list.
For Example: