Recreational & Family - Problem adding a trailer "hitch"

Hello all! I've got a Marin Muirwoods 29er. It is an "urban" bike with big wheels, street tires, and disc brakes. I recently took it in for a tune up and the LBS told me that the way my frame is built, there is no way to *safely add the side mount for my Pacific trailer. They said it's because my frame isn't flat. Has anyone else ran into this? If so, how did you deal? They told me that there might be a longer skewer, but I can't seem to find anything like that. Thanks in advance for any help!

My Burley came with a hitch that was supposed to attach to the chainstay & seatstay on the left side, fortunately Burley sells a hitch that attaches to the axle on the left side.
I did not have any issues changing it out. I don't know if such a thing is possible with your equipment or not.
I tried to find a picture of your trailer online,but I couldn't tell how it was supposed to attach.
BTW I didn't need a longer skewer to change the hitch,or more correctly I didn't use a longer skewer.

The attached image is my skewer. It is 17 cm of "usable" length (before the spacer). Does anyone know where I could get a longer skewer? Perhaps even a centimeter longer? Is there someone out there that could custom make me one? Skewers seem pretty simple... again, any input is helpful. This could keep me from having to buy another bike!

Try a search for chariot second bike hitch. It should come with a longer skewer. I don't remember if it's longer than 17 cm though.

Does the mount look like this?
http://www.escstores.net/ProductImages/Vendor5ALL/SA074_large.jpg
Unless the bike has some rather odd dropouts, just turn the mount so the large hole is below or behind.
Maybe some pics of the left rear dropout and the mount may make things a little more clear

If you need the longer skewer:

The 160mm spacing is specific to Santana built tandems AFAIK.

Try the larger tandem shops. GTGTandems (http://www.gtgtandems.com/parts/fix.html) is one.