In the specific case, the WLAN key contained a German umlaut “ü”. It was possible to use it without problems from a Windows computer, but impossible to even enter the “ü” into the WLAN key form field in OS X. The WLAN router in which that key was set up was an Astoria DSL Easy Box from Vodafone.
There probably is a variant how to connect a OS X computer to such a WLAN, without changing the WLAN key. For that to work, one has to enter the WLAN key as hex number, not as text, because in that variant entering special characters is possible. OS X will convert an entered text to hex for saving, anyway. Procedure to apply this solution (untried so far):
- First, one has to find out the hexadecimal format of ones WLAN key. For that, install “WirelessKeyView” (freeware) on a Windows PC which is connected to the concerned WLAN. See also the instructions for WirelessKey View. Probably, it is installed by simply unpacking into a directory, without a setup program.
- Now start WirelessKeyViewer. In column “Key (Hex)”, it will show the hexadecimal WLAN key in a row corresponding to the WLAN name.
- Note that hex WLAN key and enter it as WLAN key on the Mac, right into the same form field where the text key would go. But, important: prepend the hex key with the two character string “0x” (uero, X). This lets OS X recognize that this WLAN key is in hex format instead of the regular text format.
- And instead of typing the key (which can be 64 characters prone to typos), you could also transfer it via a file and then the clipboard from WirelessKey Viewer to the Mac’s form field.
No guarantees, but this should work. Sources: