Error using plm package pooltest: Error in FUN(X[[i]], ...) : insufficient number of observations


I am analyzing panel data and am trying to use pooltest(). My data is balanced and I have successfully been able to use plm(), pdata.frame(), phtest(), but for some reason when trying pooltest with exactly same data i receive error message: Error in FUN(X[[i]], ...) : insufficient number of observations.

This is what I have used:
pooltest(ResProd ~ Agri + Indus + Manuf + Const + ServSec + Pop + GDP + EnvTax + RDExp, data=pdata, model="within")

And these have worked fine:

pdata <- pdata.frame(data_w2, index=c("c_id", "t_id"))
pooled <- plm(ResProd ~ Agri+Indus+Manuf+Const+ServSec+Pop+GDP+EnvTax+RDExp, data=pdata, model="pooling")
fe <- plm(ResProd ~ Agri+Indus+Manuf+Const+ServSec+Pop+GDP+EnvTax+RDExp, data=pdata, model="within")


Can anyone help? Why am I getting this error message?

To specify, I am using plm package and my data set consists of 665 obs. of 14 variables, more specifically 10 independent variables.

My analysis is on 35 countries over 19 years.

Thank you!