I have always had sporadic crashing to desktops on Isengard instances, but they weren't common so I tolerated them, but ever since U7 every Isengard instance I have entered I have crashed upon loading. I have to restart the game to get into my instance which takes a long time. I have windows 7 and every other instance runs fine, Turbine please fix these buggy isens.
I don't do Isen myself - mostly needs group, so it's not high on my to-do list. However, I have seen another forum poster complaining about a similar symptom. In their case, it turns out to be an incompatibility with their current sound set up. You might want to try playing with the sound off for a while, as an experiment, to see if stability improves.
as mentioned above muting ingame sounds during transitions seems to be a temporary fix for many. Alternately you may also try updating your video card drivers, I had crash to desktop issues tho not on transitions and updating my drivers to latest beta drivers fixed my issues completely, YMMV.
Nope muting doesn't work, it is not something wrong on my side for sure, crashing has been getting far more constant after U7. My drivers are all fully updated as well.