Residence permit issue -holding alien employement permit

Hi,
Three months ago,I got the alien employement permit in shenzhen,but then police station in luohu refuses to deliver the last paper for my residence permit application.
I was forced to leave China.Now i am back with a M visa,still have my employement permit valid until sept 2014,is it illegal if i end up working again for my same employer? i really do not know why my residence permit application got rejected.I have never been in trouble in China,i studied there for 3years before