There was a critical license related bug in mental ray 3.7 on Intel Core i7 and the fixed version seems to be distributed now.
The fixed mental ray (SPM) version (might depends on OEM) is the following.
mental ray 3.7: 126.96.36.199 (2009 September 16) or higher
mental ray 3.7+: 188.8.131.52 (2009 October 22) or higher
The detail of this problem is: When you want to run mental ray on Intel Core i7 machine, you will get the following error message:
Sorry, no license available
and can not run mental ray even you have enough licenses left.
It seems recent Intel's CPU becomes complex to count the number of cores. This bug seems related with this.
Personally, I don't like the license that limits the number of cores. Because the new machines has more cores, but we can not use these cores because of license shortage. If I buy a new machine, I expect that the software runs faster or more comfortable to use. On the other hand, there is no such limitation for GPU that has a lot of cores inside. NVidia/mental image's new renderer 'iray' seems no such limitation for number of cores. I don't know why CPU and GPU have different licensing method. It is just a historical reason, or they are promoting GPU. But, then, Intel or AMD might sue such a license. Fro the users, it is not so great to be suffered by such a strange licensing form.
I believe if you have a problem with mental ray on an Intel Core i7 machine, you could get the updated version when you asked to the support. But, if the support doesn't know this problem, I recommend to refer the above mental images official forum's link and request the fixed version of mental ray.