Version 2.2.0 of the rjags package for R is now available on CRAN. Previously, the version of rjags for Mac (2.1.0) was incompatible with the latest release of the JAGS library (2.2.0). Let me know if you have any further problems. I’m not a Mac user myself. In fact JAGS on Mac would not exist at all without the help of Bill Northcott, who makes binaries of the JAGS library, and Simon Urbanek who builds the Mac OS X binaries for all R packages on CRAN.