Hi , I don't know whether it is a Mac specific problem. I hope it does not bother you. When I start R each time I got the following warning , I reinstall for many times the problem still exists. R(4053,0xa0619fa0) malloc: *** error for object 0x15630350: double free *** set a breakpoint in malloc_error_break to debug R(4053,0xa0619fa0) malloc: *** error for object 0x15630f10: double free *** set a breakpoint in malloc_error_break to debug R(4053,0xa0619fa0) malloc: *** error for object 0x15630350: double free *** set a breakpoint in malloc_error_break to debug R(4053,0xa0619fa0) malloc: *** error for object 0x15630f60: double free *** set a breakpoint in malloc_error_break to debug My sessionInfo() is > sessionInfo() R version 2.7.0 (2008-04-22) i386-apple-darwin8.10.1 locale: zh_CN.UTF-8/zh_CN.UTF-8/C/C/zh_CN.UTF-8/zh_CN.UTF-8 attached base packages: [1] stats graphics grDevices utils datasets methods base -------------------------- Peng Jiang ?? Ph.D. Candidate Antai College of Economics & Management ???????? Department of Mathematics ??? Shanghai Jiaotong University (Minhang Campus) 800 Dongchuan Road 200240 Shanghai P. R. China