The only thing I would suggest is Backup your data and then run a Re-Index from the File... Maintenance menu selecting Sales Orders and possibly Stock

Thank you for the suggestion Ken, I'll give it ago and see how it is afterwards.

Are you completely up to date with your Sage version? 
We were experiencing this, along with other random crashes until we updated to the latest version.

But there is also a discussion on here regarding random crashes with version 29.

Hi Robert, 

Thanks for using Sage City!

Does this crash occur only when manually allocating Sales Orders?

I would advise:

- checking if the same issue occurs with other usernames

- checking your data for any errors by going to File > Maintenance > Check Data and if there are errors, using this guide https://desktophelp.sage.co.uk/accounts/errors/ to resolve them

- log into Demonstration Data by going to File > Open > open Demo Data and if prompted, log in with MANAGER and no username. If the same issue occurs in here, you will need to uninstall and then reinstall your Sage program, preferably the latest version v29 if possible.

- If Demo Data is fine, and the issue only occurs with one username, then it will be an issue with criteria files for that username, which can be resolved following this guide here https://gb-kb.sage.com/portal/app/portlets/results/viewsolution.jsp?solutionid=200427112338742 

If this has helped, please click the ellipsis ...,, and click Verify Answer.

Regards,

Shaun

Sage UKI

Good Afternoon Shaun,

This is not a user related issue, it is happening with multiple users within the company on various different PC's. Still can't seem to get this fixed.