[R] Singular error in rlm

[uttara_n]

I am absolutely new to R and I am aware of only a few basic command lines. I
was running a robust regression in R, using the following command line

library (MASS)
rfmodel2 <- rlm (TotalEmployment_2005 ~ ALABAMA + MISSISSIPPI + LOUISIANA +
TotalEmployment_2000 + PCWhitePop_2005 + UnemploymentRate_2005 +
PCUrbanPop2000 + PCPeopleWithACollegeDegree_2000 +
PCPopulation.of.or.over.65.years.of.age_2005)
summary (rfmodel2)

But, it keeps giving me an error message as soon as I try to run it
Error in rlm.default(x, y, weights, method = method, wt.method = wt.method, 
: 
  'x' is singular: singular fits are not implemented in rlm

I used the above mentioned command line previously and it worked fine, but
after I deleted a few observations, it started giving me this error. I even
tried to change the setting to --no restore data- but that did not work
either.

I am a beginner, so it would be really helpful if someone could explain this
error to me.
Thanks!
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