LATEX ERROR: paragraph ended before \@citex was complete

While I was compiling my paper with ACM sigplan template, I get a lot of error messages like this:

paragraph ended before \@citex was complete

I could only know there is something wrong in citations/references. But, I had no clue of how to fix it.

I firstly read the Author’s Guide to the ACM SIGPLAN Class (sigplanconf.cls). It states that SIGPLAN class wants the bibliography to be included in the main LATEX file. So, I merged my BBL file to the main tex file, as the author's guide suggested. However, it did not solve the problem.

After trying to remove many different parts of my article, I finally find a way to successfully build my paper

comment out \usepackage{cite}. 

I do not know if this is bug of the class file or if I am not using it properly. I would be happy to know why the "cite" package conflicts with the sigplan class file. Before that, I am happy that I can keep compiling and writing my article now.

Picture today: Manhattan, NYC. [courtesy of my dear wife - Claire Huang]