[R] plm summary error

[Ulrich Morawetz]

Dear "plm"-Package insiders, 
  
[I posted the following observation is April already but unfortunately I am not aware of any answers. 
With the hope that someone found an answer in the mean time, I ask again:]

I realized the following difficulty with the summary.plm function (demonstrated with the example from the ?plm documentation).       

library(plm)   
data("Produc", package="Ecdat")   
estimation_method<-"within" 
estimation_effect<-"individual"   
     zz <- plm(log(gsp)~log(pcap)+log(pc)+log(emp)+unemp, data=Produc, index=c("state","year") 
, method=estimation_method 
, effect=estimation_effect 

    ) 
     summary(zz) 

 #Error: object of type 'symbol' is not subsettable   

#But if I run   
 
    zz <- plm(log(gsp)~log(pcap)+log(pc)+log(emp)+unemp, data=Produc, index=c("state","year")
, method="within"
, effect="individual"
) 

summary(zz) 
#the summary function works fine.   



Is it wrong (or bad practice) to define the function's parameters as I did in the upper example? If yes, how should it be done correctly such that the summary function works?   

I am running R version 2.9.1  wie plm version 1.1-4 on a Windows XP workstation.   I checked, and the same issue occurs under Linux (Ubuntu).

Thank you for your advice, Ulrich Morawetz