The first reason of this error is that soure file is not a valid MS Access database. The second reason could be missing appropriate Microsoft Data Access (DAO) libraries on the system to read the database. In this situation it is recommended to install Microsoft Access Runtime as it contains correct version of DAO libraries:
NOTE: if you have 64-bit version of MS Office or Access installation, it is still required to download and install 32-bit versions of Access Runtime.
If the error persists contact Intelligent Converters support.