There are two known reasons that this error can occur:
On Windows, HDFView was built with VS, and it requires that the Visual C++ Redistributable Packages be installed on your machine. If you cannot access HDF5 files then you do not have these packages. You can obtain the latest supported Microsoft Visual C++ downloads HERE.
This error can also occur if there are unicode characters in the path or name of the HDF5 file. If you remove the unicode characters from the file and/or path, it should correct the problem.