My first thought would be that while you are writing the data, the location of the data being written might be different on those systems. For example, the user might not be using that specific locale ID of software, It might be best to use the "CurVer" key (in HKLM) to extract the current version, then use that to find the locale ID from the CurVer key under that key (in HKLM not HKCU) ... once you have that data, you can then place the information in HKCU in the proper location. Also, you might look at the registry of an installation where it worked and one where it did not. There may be another entry in HKCU or HKLM that specifies which is the default setting for ETransmit.
for example, check under the setups item to see if there is anything in there.
I have attached a zip file containing a VBscript to get the AutoCAD installation information and display it to the user. If you look at how I did it htere, you might get a little bit of insight on how I would tackle it.