I've tested the R2.12.x versions xlsReadWrite 1.5.4 and xlsReadWritePro 1.6.4 with the new R2.14.0 and they run well.

There would be minor updates to both packages but I currently do have problems compiling the C-based placeholder dll (for CRAN) with R2.14.0. It works fine in R2.12 and R2.13 but no longer in R2.14. It's probably due to the fact that I use a cygwin based toolchain instead of the R-specific MinGW etc. Some error messages also surfaced in other projects and - considering the minor package updates - I think I am lazy now and wait for the eventual R2.14.1 update which may fix things. I'll also will try to get rid of the placeholder dll altogether and avoid these troubles.