On top of the above, please confirm that you have the Oracle 64bit driver installed on your machine.
For migration scenario from Legacy to Windows, it is important to mention that the Windows project uses only the 64bit database drivers.
The dependency is also an important factor, of course. The legacy projects used the Oracle.ManagedDataAccess dependency, while the Windows projects use Oracle.ManagedDataAccess.Core dependency.
The the case of Database 1.9.0 package, these are:
