When opening Omnigraffle file, getting a "You don't have permission" error

When I try to open an Omnigraffle file in Version 7.4.1, I get an error message saying it could not be opened because I do not have permission. However, if I go to Get Info on the file, it says I have Read/Write access.

Anyone know if this is a known issue or how to fix it?

Sorry about the inconvenience caused by this issue. We have had some reports of this problem happening in the first OmniGraffle session after applying macOS updates. We are looking for a way to consistently reproduce the issue so that it can be addressed. Quitting and relaunching the application should solve the problem.

If you are in the middle of editing a document, choose Contact Omni under the help menu. Uncheck anonymize data, and attach your document, then change the email from Omni to yourself. That will email your work to the address chosen. Once you have received your document, quit OmniGraffle and relaunch. If relaunching does not resolve the issue, or if this happens at a time other than after applying macOS updates, please contact us so that we can suggest more detailed troubleshooting steps.

Hello, when using the latest version of OmniGraffle 7.18.2 with Mac Big Sur 11.2.1, the error “You don’t have permission to open the application” is presented. Please advise as to any work arounds. Thank you.

So after a little bit of investigating, removing Omnigraffle and re-installing from the App store seems to alleviate the issue.