We can reproduce your DOMAIN ERROR.

You are on the right track by mentioning ⎕DL.

We have looked at your code and suggest a ⎕DL 0.1 after the ⎕EX 'F.C' in ChangeClipboard.

I think that this gives a chance for Windows messages to come through and be processed. I have tested and it fixes the DOMAIN ERROR.

Regards,

Vince

Dyalog Support