This problem is rare and most likley to be encountered on a new install.I am addding it here so that there is a permenant record of the problem and solution.  After the R6 install, R6 will not open and gives an unhandled error. Inspection of the Call stacks in the error log will show that R6 was trying to get the application setting and that it has faile to get language.extref.  This suggest that R6 has been set up to use a language which it does not support. The solution is to change the language in Windows to UK or uS English.