Since I upgrade to 8.1.22 it occure sometimes that issue, I have to restert Ignition service to fix that.
Can you post the full error message with the stack trace? (click on the "full" link in the dialog). Also, if you post it as text (click on "copy"), it's much easier for us to help solve this.
Is there any particular thing you are copying that tends to cause this?
I will send you full report soon as I got error again, the error occured at a view opening.