To correct the permissions issue, locate the “userdic.tlx” file in the SysWOW64 folder location and update the “(Workstation Name)\Users” group to have “Full Control” permissions on the file. Once the permissions change is made, you should be able to add the word to the dictionary without issue.
The catch is since Windows® does not allow writing to the system location; the operating system automatically moves the file to the following location “C:\Users\CAS\AppData\Local\VirtualStore\Windows\SysWOW64” (CAS being the user name logged in with this example). With the file in this location, the “CAS” user is now able to modify the file as needed.
We do not have the resources to test altering permissions on a domain level, but suspect changes made at this level may not allow the updating of the files in question at a local workstation level. You may need to conduct additional testing (using the above provided steps) to identify the permission changes needed in your own environment.