Just recently upgraded ( without uninstalling 10.2 ) to 10.4 in my Windows 7 Professional SP1 64 bit machine and starts throwing this error upon opening ArcCatalogue.
It doesn't show with ArcMap. Noticed some tools not working and so does searching.
Some issues with a 64-bit machine ? .. Because a colleague installed 10.4 with a 32-bit machine with no issues.