SharePoint 2010 List Workflow cancels on one device, works fine on anothe for same account

I'm facing a strange issue with a list Workflow that I've built in SPD. The Workflow is responsible for sending an email to speficic recipients based on 2 lookup fields (choice drop down). 1 of the fields is mandatory and it's not causing any trouble but the other one is optional and any time I add an item to the list which doesnt have a selected choice the WF gets cancelled. The thing is that a more experienced person got to the root of the issue and the outcome is that the WF is now working fine for all users except me in the mentioned case. The weird thing here is that I logged on with my account to the SharePoint site on my friend's laptop and the WF works without any errors. I try again the same on my device and I get the same result - the WF gets cancelled in any case where I don't have anything selected in that field.

I hope anyone will be able to assist with this as it is really frustrating.