[R] wilcox.test warnig message p-value where are the zeros in the data?

[Knut Krueger]

does anybody know why there are the two warnings in the example above?

Regards Knut

 > day_4
 [1] 540   1   1   1   1   1   1 300 720 480
 > day_1
 [1]  438  343    1  475    1  562  500  435 1045  890

> is.vector (day_1)
[1] TRUE
> is.vector (day_4)

[1] TRUE

 > wilcox.test(day_4 
,day_1,paired=TRUE,alternative="two.sided",exact=TRUE,conf.int=TRUE)

        Wilcoxon signed rank test with continuity correction

data:  day_4 and day_1
V = 1, p-value = 0.02086
alternative hypothesis: true mu is not equal to 0
95 percent confidence interval:
 -486.5 -120.0
sample estimates:
(pseudo)median
          -348

Warning messages:
1: cannot compute exact p-value with zeroes in: 
wilcox.test.default(day_4, day_1, paired = TRUE, alternative = 
"two.sided", 
2: cannot compute exact confidence interval with zeroes in: 
wilcox.test.default(day_4, day_1, paired = TRUE, alternative = 
"two.sided",