I'd first look in the Dynamics.set file to make sure you don't have any dictionary files named what the error is referencing, which I'd be surprised if you did.
Also, if you have the dictionary files in a shared network directory and/or using an UNC path, try moving everything local, i.e. C:\Program Files(x86)\Microsoft Dynamics\GP2018R2\Data\ and change the Dynamics.set file to point to these local files. Test launching Dynamics GP again to see if that resolves the error.
If neither of the above help, next, try the following:
1. On one of the machines with Dynamics GP seeing this error, have all users log out of the GP application.
2. On this same machine, re-name the entire GP directory, from an example of C:\Program Files(x86)\Microsoft Dynamics\GP2018R2\ to C:\Program Files(x86)\Microsoft Dynamics\GP2018R2_OLD\
3. In Control Panel > Programs > Programs and Features, right-click on the Microsoft Dynamics GP instance and click 'Change'. In the options window that opens, run the Repair process. The Repair process will re-create the entire GP directory renamed, i.e. C:\Program Files(x86)\Microsoft Dynamics\GP2018R2\, without any third-party products or customizations, nor any modified forms and reports.
4. Log into Dynamics GP using this 'new' GP directory and see if we can re-create the 'Unable to open dictionary.....' error.
--If the error doesn't show, then we'd want to add back the modified forms and reports dictionary files first, testing after those to see if the error returns. If it does return, then it is a matter of figuring out which dictionary is corrupted and needs to be fixed.
--Then, add back any third party products or customizations, one-by-one, testing after each one, to see if the error comes back indicating there may be an issue with that product or customization.
Let us know what you find out or if you have any questions.
Thanks
