Gerring error in biwavelet package

Hi All

I am running the following commands-
t1 = cbind(date, vix)

t2 = cbind(date, tc)
nrands = 1000
wtc.AB = wtc(t1, t2, nrands = nrands)
I got the following error-
Error in check.datum(y) :
The step size must be constant (see approx function to interpolate)

Can someone please help me to resolve.

Thank you in advance.