[R] problem fitting 2 term exponential with nls

[Tom Wright]

Hi,
Can anyone explain why the nls function is giving an error?
Thanks
Tom

> head(d)
        age  time
1 23.566667 223.0
2 42.633333 223.0
3 62.300000 222.0
4 32.933333 220.5
5  9.366667 228.0
6 23.833333 227.0

> fit<-nls(d$time~a1*exp(b1*d$age) + 
	a2*exp(b2*d$age)+c 
	,start(a1=10,b1=0,a2=250,b2=1,c=0)
	,trace=T)
Error in hasTsp(x) : argument "x" is missing, with no default