This issue happens due to your antivirus blocking Access UBS. To resolve a bad association error when opening the database, there are two possible solutions. Please follow the steps below:
Close Access UBS,
Open your antivirus software and make exceptions for ‘UBSACC2015’, 'UBSSTK2015', and 'UBSCPL' folders in the C drive.
You can also try uninstalling and reinstalling your antivirus software.
OR
If the steps above don't work. You may try to uninstall and reinstall the UBS.
Installation guide: Access UBS: How to Install Access UBS software?