[R] R-2.2.0: aggregate problem

[jfontain@free.fr]

> aggregate(as.ts(c(1,2,3,4,5,6,7,8,9,10)),1/2,mean)
Time Series:
Start = 1
End = 9
Frequency = 0.5
[1] 1.5 3.5 5.5 7.5 9.5
> aggregate(as.ts(c(1,2,3,4,5,6,7,8,9,10)),1/5,mean)
Error in sprintf(gettext(fmt, domain = domain), ...) :
	use format %f, %e or %g for numeric objects
>

I must be doing something wrong, but what?

Many thanks for your help,

--
Jean-Luc