This is typically caused by insufficient permissions to the Shared Data folder and / or insufficient access to the trunk of the registry pointing to the shared data folder. 
As a test, try running Sage as administrator, then open your custom screen. 

I tried running Sage as Administrator.  Same error.

I think it has something to do with the workstation but not sure what or how to find it.

I checked the permissions on the shared data folder and they are the same as the other 9 workstations which all work okay.

This workstation is the only one with multiple screens.  Not sure how that would affect it.  I had them remove the second screen and no change.

Not sure what they did when they removed the screen though.

PITA

UAT can give this issue, especially when the session manager is running under a different security context. But running as Administrator should have worked around that.

Check the path environment variable.

And how are you running your screen?  As a Program icon?  Depending on what your screen is doing, you might need to set the Start In path in addition to the command line.

Just to confirm - logging on as the user who's workstation is causing grief, on a workstation that works, exhibits no problems.  And vice versa - just to solidify that the workstation is the issue and not a network profile issue or a Sage 300 profile issue.

Are you loading the OCX dynamically or have you embedded it within the .exe?  If embedded, could your .exe be trying to access two versions of the OCX or TBL file that do no exist where this workstation can see them (but the other workstations can).

Re-run Workstation setup (or uninstall Sage and re-install).

Any service pack discrepancies?

And, just because, have you tried turning the computer off and on again?

Would also be a worthwhile exercise to re-confirm the basics:
Path pointing the correct (and only one) runtime folder
Registry programs and shared data values are correct
I'd also echo Django's suggestion regarding re-running workstation setup

I'll have a look at user account control but I think I changed that.  I usually do.

I've logged on the workstation as the domain administrator and logged into Accpac as the ADMIN.  Same issue.

I reviewed all the registry settings and the path.  All okay.

I've not logged onto another workstation as the user.  I will try that this evening.  I expect it will be fine but we'll see.

The OCX is embedded in the .exe.  None of the workstations can see the old one.

I will re-run workstation setup for the nth time.  I've restarted the workstation many times and will do so again this evening.

Thanks Django.  I do appreciate your help and Jay's.

Dana

I'll have a look at user account control but I think I changed that.  I usually do.

I've logged on the workstation as the domain administrator and logged into Accpac as the ADMIN.  Same issue.

I reviewed all the registry settings and the path.  All okay.

I've not logged onto another workstation as the user.  I will try that this evening.  I expect it will be fine but we'll see.

The OCX is embedded in the .exe.  None of the workstations can see the old one.

I will re-run workstation setup for the nth time.  I've restarted the workstation many times and will do so again this evening.

Thanks Django.  I do appreciate your help and Jay's.

Dana

Last suggestion I can think of - open the stock OE screen.  Sounds basic, but has gotten me over the hump many times.

I uninstalled and reinstalled workstation setup for about the 6th time and it now works!  

I doubled checked all the settings in the registry, path, etc.  I did shut off the UAC.

Painful install but I'm cautiously optimistic it will continue to work.

Thanks Everyone for your help.