Odd error in expand.grid()

I've created and evaluated a call to expand.grid by using eval(parse(...)).

In short:

len <- 36
Text <- paste("pos <- expand.grid(",
  paste(rep("c(TRUE,FALSE)", len), collapse=","), ")", sep="")
eval(parse(text = Text))

Gives me

Error in rep.int(rep.int(seq_len(nx), rep.int(rep.fac, nx)), orep) : 
invalid 'times' value
In addition: Warning message:
In rep.int(rep.int(seq_len(nx), rep.int(rep.fac, nx)), orep) :
NAs introduced by coercion

as opposed to len number of combinations of TRUE/FALSE in the variable pos.

I am overlooking something simple, or maybe not...?