I upgraded to windows 8 and outlook 2013 and when I click on send email from a CommitCRM ticket, I get an error in outlook saying The command line argument is not valid. verify the switch you are using.
Does this happen on a PC that had a previous version of Outlook installed? Also, please try to run RangerMSP as Administrator (right click the RangerMSP.exe file for this) and see if it makes any difference.
