SME is pretty stable on its own, but hardware can have problems, as does software you might have added thats not included with SME. Bad ram or conflicts with the PCI cards happen often.
I would try creating a boot disk using this ram test software:
http://oca.microsoft.com/en/windiag.aspDont worry, it doesnt require Windows or anything. Its just an excellent ram test that has caught several bad sticks of ram for me. I run it on all the systems I build.
If you run it thru the extended tests once or twice with no errors, your system is good, but you can still have a problem with the other hardware like the nics or hard drive.