Suddenly my project started to do the following error, I have no clue why

"c:\program files\miktex 2.7\tex\generic\pgf\modules\pgfmoduleplot.code.tex(1): Package fancyheadings Warning: Please stop using fancyheadings!
"c:\program files\miktex 2.7\tex\generic\pgf\modules\pgfmoduleplot.code.tex(2): Error: ! Text line contains an invalid character. (and repeats this error in the output window 100 times)