R error in updating formula when using variable named 'x':

R error in updating formula when using variable named 'x':

References

Reference NO 1

http://stackoverflow.com/questions/15202218/r-error-in-updating-formula-when-using-variable-named-x

Reference NO 2

http://stackoverflow.com/questions/11510976/change-the-name-of-a-variable-in-a-formula

Reference NO 3

http://r4stats.com/2012/09/25/specifying-variables-in-r/

Reference NO 4

http://stat.ethz.ch/R-manual/R-patched/library/stats/html/formula.html

Reference NO 5

http://data.princeton.edu/R/introducingR.pdf

Reference NO 6

http://cran.r-project.org/doc/manuals/R-intro.html

Reference NO 7

http://www.r-bloggers.com/r-3-0-0-is-released-whats-new-and-how-to-upgrade/

Reference NO 8

#EANF#