This is a bit of a reach, and probably won't be helpful, but I see you've customized your lookup. Does the same thing happen on the Standard (non-customized) lookup? All lookups or just the Item List? Oh, and I assume you've had the user follow the steps to sign into Office 365 - just to cover all the bases?

Hey Cullen. Looks like the latest windows update left an office 365 client app running in the background. When the user clicks on the option the app forces an attempt to subscribe. Their IT guy was able to remove the app, now item inquiry no longer throws an error and the export to Excel is now working properly.

Hey Cullen. Looks like the latest windows update left an office 365 client app running in the background. When the user clicks on the option the app forces an attempt to subscribe. Their IT guy was able to remove the app, now item inquiry no longer throws an error and the export to Excel is now working properly.

do you know what that O365 app was that got removed?