You may be running into the following error when uploading a user from the device: 

Or the error below when adding enrolling a user template with a device:

This will occur if you're using the MSSQL version of BioStar 2 and do not have the proper Native Client installed. 

This happens because your client PC's ODBC driver version is lower than the server PC's ODBC driver. 

Starting in BioStar 2.5.208 (hotfix version) the manual states that you have to install the native client in your client PC:

Note for MS SQL users (as shown in the manual note)

If you are using MS SQL Server 2012, install the SQL Server Native Client by referring to the following web page. If MS SQL Server and BioStar 2 are installed on different PCs, you should install the Native Client on a PC with BioStar 2 installed.

Refer to the system requirement article or the admin manual: 

[BioStar 2] System Requirements / Supported Operating System

You can also refer to the announcement below: 

[BioStar 2] Issue caused by ODBC Driver (MSSQL)

If you faced the same error while using MariaDB, it might be because of the start date and the end date of a user. Please make sure that the start date is not earlier than 01/01/2001 and the end date is not after 31/12/2030 before you upload the users.