Do you have the MC shell extension activated. options-->general-->shell options wouldn't think it would matter but ?
Curious what mouse brand/model are you using?
I've tried toggling the shell extension options to no avail.
I've now got 4 different dell machines here:
One XPS M1530 Laptop (Windows 7 Ultimate)
One Dimension E521 Desktop (Windows 8 Consumer Preview)
One Vostro 200 Desktop (Windows XP)
One Optiplex 360 Desktop (Vista Business)
All these machines are exhibiting this same problem with clean installations of MC17 and my MC16 portable installation.
I've just installed MC17 on the 4th Dell machine. This time a Windows Vista machine with the task bar in classic mode Windows XP style mode with Aero turned off. Same again no right click. One thing I've noticed is that very occasionally it does start working, but a left click on the icon to either show or hide MC then prevents it from working again.
Here's the clincher.. The Vostro has MC13 installed from way back when. MC13 is not exhibiting the same problem.
So what ever this issue is it started somewhere between 13 and 16. (Assuming no settings change in MC13 which effects the issue)
The mystery is why no one else is seeing it ?
I believe the following is related:
http://yabb.jriver.com/interact/index.php?topic=70817.0When the issue is present no controls pop up on the MC Preview Pane in Windows 7/8