Welcome to TeX.SE. This problem is probably due to some other error, so it would be helpful if you composed a fully compilable MWE including \documentclass and the appropriate packages that reproduces the problem for you.
– Peter GrillFeb 23 '13 at 19:43
10
If you use MiKTeX, your problem may be explained in the following post: http://tex.stackexchange.com/q/96778/19384
– Peter JanssonFeb 23 '13 at 20:02
If nothing else works, you can always make a new installation, but this is og course as a last resource.
– Svend TveskægApr 04 '13 at 12:57
If you use TeX Live, does kpsewhere amsmath.sty in a terminal window print out the path to amsmath.sty?
A MWE of your code would be nice to find out, if there's another source for this error message.
– Stephan LukasczykApr 04 '13 at 15:12
\documentclassand the appropriate packages that reproduces the problem for you. – Peter Grill Feb 23 '13 at 19:43kpsewhere amsmath.styin a terminal window print out the path to amsmath.sty? A MWE of your code would be nice to find out, if there's another source for this error message. – Stephan Lukasczyk Apr 04 '13 at 15:12