Building R package with Reference objects fails - r

Question

I recently rewrote a package to use the new(er) R reference class objects. I've exported the three classes using export() in the NAMESPACE file so as far as I'm aware that should work. However when I test build the package I get an error at lazy loading stage:
** preparing package for lazy loading
Error in file(con, "rb") : invalid 'description' argument
ERROR: lazy loading failed for package ‘PACKAGE_NAME_HERE’
* removing ‘/Library/Frameworks/R.framework/Versions/3.0/Resources/library/PACKAGE_NAME_HERE’
I'm not sure what the problem is here. I don't know if it's relevant but the reference classes do store data on files in the tmp directory by having some fields set as accessor functions - I don't know if that's what s being complained about here when it says (con, "rb") which I guess is some connection thing. Does anybody have any ideas or advice for making sure reference classes get exported properly? My namespace is currently simple -
export(Main)
export(Mainseq)
export(Maintriplet)
Which are the three reference classes I exported by using #export tags in roxygen2.
What is it I'm doing (or not doing) that is throwing the lazy load error?
(ASIDE - I have no compiled code - all R, although the reference class methods do call some internal functions that are not exported, but these are supposed to be internal so I don't think I need to export them.
Thanks,
Ben.
EDIT:
My description file is as follows:
Package: HybRIDS
Type: Package
Title: Quick detection and dating of Recombinant Regions in DNA sequence data.
Version: 1.0
Date: 2013-03-13
Author: Ben J. Ward
Maintainer: Ben J. Ward <b.ward#uea.ac.uk>
Description: A simple R package for the quick detection and dating of Recombinant Regions in DNA sequence data.
License: GPL-2
Depends: ggplot2,grid,gridExtra,png,ape
I can't see what is wrong with this - the Depends are correct.
EDIT:
I've eliminated the first error with the description but I'm still getting the con error.
I think it's because the Mainseq class (which is nested in class Main) has some fields:
FullSequenceFile = "character",
FullSequence = function( value ) {
if( missing( value ) ){
as.character( read.dna( file = FullSequenceFile, format = "fasta", as.matrix = TRUE ) )
} else {
write.dna( value, file = FullSequenceFile, format = "fasta" )
}
},
InformativeSequenceFile = "character",
InformativeSequence = function( value ) {
if( missing( value ) ){
as.character( read.dna( file = InformativeSequenceFile, format = "fasta", as.matrix = TRUE ) )
} else {
write.dna( value, file = InformativeSequenceFile, format = "fasta" )
}
}
The idea being upon initialisation, the two character fields are filled with a path to a temp file in tmpdir, and when the variables are called or edited the files containing the variable data are read or written to. However it seems the variables are being accessed before this path is available because up package build the following happens:
** preparing package for lazy loading
Warning in file(con, "rb") :
cannot open file '/var/folders/kp/clkqvqn9739ffw2755zjwy74_skf_z/T//RtmpLB8ESC/FullSequenceaba52ac591f3': No such file or directory
Error in file(con, "rb") : cannot open the connection