That's a strange one!
I'm using 2.5.16 on Windows XP here and I did the following.
1/ Checked that double clicking a PTG file worked with ArtRage in the default Start Menu location.
2/ Created a folder in the Start Menu called "Graphics"
3/ Moved my ArtRage folder in the start menu into Graphics so:
Start->All Programs-> Graphics->Artrage 2->ArtRage shortcut is here
Note: I'm not using classic menus, just the XP default here
4/ Double clicked a PTG file to verify that ArtRage still launched.
Let's see what we can find out.
Firstly, the latest version of ArtRage is ArtRage 2.5.16 - Can anyone verify that they can duplicate the problem with this version? I have also tried uninstalling my copies of ArtRage here and doing a 2.5.15 install, then moving the folder as above but so far haven't been able to duplicate this.
Also, if someone is running 2.5.16 and has this problem, please let me know if possible:
The operating system
What style of start menu you're using if it's Windows XP/Vista ( Classic or default )
What user permissions you have ( Administrator or other )
Any differences in the steps to reproduce the problem from your own and mine above, even if they seem minor like the final folder structure in the Start Menu, names of folders etc.
We'll also have a look here into how the .msi works.