[R] tkconfigure throws an error

[stephen bond]

Thanks everybody for looking at this. I am trying to assign a script to 
a button
please help:

############
library(tcltk)
tt<- tktoplevel()
tktitle(tt)<-"the title"
heading<-tklabel(tt,text="Enter date as YYYY-MM-DD")
l1<-tklabel(tt,text="Reporting date")
b1=tkbutton(tt,text="Run")
d.val<-tkentry(tt,width=12)
tkgrid(heading,columnspan=2)
tkgrid(l1,d.val)
tkgrid(b1,columnspan=2)
tkconfigure(b1,command=source("./src/f.imm2.R"))
#########
and get inconsistent errors:
1. Error in structure(.External("dotTclObjv", objv, PACKAGE = 
"tcltk"), class = "tclObj") : 
	[tcl] invalid command name ".6.4".  ## when the tkconfigure is 
entered from R buffer
2. tkconfigure(b1,command=source("./src/f.imm2.R"))
Error in switch(storage.mode(x), character = .External
("RTcl_ObjFromCharVector",  : 
	cannot handle object of mode 'list' # when I run the full source 
buffer (stuff pasted above)

the script just needs the date from the tcl window and everything else 
is conventional R code.