R quantreg basksolve错误

Question

当我在R中安装quantreg包时，我收到此警告：

> library(quantreg)
Loading required package: SparseM
Package SparseM (0.96) loaded.
       To cite, see citation("SparseM")


Attaching package: 'SparseM'

The following object(s) are masked from 'package:base':

    backsolve

Package quantreg (4.79) loaded.
        To cite, see citation("quantreg")

然后，在运行分位数回归后：

sym.lm  = rq(Y ~ X1 + X2 + X3 + X4 + X5 + X6 + X7, data = myd, na.action = na.omit, method = "fn", model = TRUE)
summary(sym.lm)
Error in base::backsolve(r, x, k = k, upper.tri = upper.tri, transpose = transpose,  : 
  singular matrix in 'backsolve'. First zero in diagonal [1]
In addition: Warning message:
In summary.rq(sym.lm) : 21010 non-positive fis

此错误是否与backsolve范围问题有关？