I have also seen that message. When I do, I can get around it by scanning at a lower resolution. Not ideal for certain documents, but for the majority of things I scan it works.
Same problem here! We use the Canon DR-C225 (which I love). I thought it was a Canon issue but it is now obvious it is a Softdent problem. Hopefully, with all these comments, they will figure this out.
Would this work as a workaround:
Scan the document to the computer, but not directly into SoftDent. Then within SoftDent, open the patient's documents and select "Capture New Document" and follow the prompts to import that scanned document.
It's definitely a work-around, but maybe it'd save you from re-booting the computer?