Access 2010-2016 Compatibility Error

I was just updated to Access 2016, while my users are still at Access 2010. I opened our database in MS Access 2016 once, didn't make any changes, and closed it out, and now all the users are having errors for **ANY** basic VBA code, including: StrConv (Me.FormField, vbProperCase) DoCmd.GoToRecord DoCmd.RunCommand acCmdSaveRecord etc. However, it works fine on my end. Totally broken for all my users on Access 2010. Is there any way to fix this? I am thinking, even if I go back to Access 2010, if these are errors for code that would normally work fine in either version, how to I resolve these errors? Tried a compact and repair, no effect. Here's an example: In Access 2010, when the AfterUpdate() event is triggered on a textbox that has the StrConv (Me.FormField, vbProperCase) function, it brings up the VBA debugger. The error is: **Compile error: cannot find project or library.** Previously, the exact same function worked fine in access 2010, and there have been no changes to this code. It works fine in a backup copy from about 15 days ago.