[BioC] Error: package/namespace load failed for 'affy'

[Sebastien Gerega]

Hi,
when loading library "affy" I am getting the following error:
Error : package 'preprocessCore' does not have a name space

I am running R on a PC running 64 bit Windows Vista and here is my 
sessionInfo:
R version 2.8.0 beta (2008-10-05 r46601)
i386-pc-mingw32

locale:
LC_COLLATE=English_Australia.1252;LC_CTYPE=English_Australia.1252;LC_MONETARY=English_Australia.1252;LC_NUMERIC=C;LC_TIME=English_Australia.1252

attached base packages:
[1] tools     stats     graphics  grDevices utils     datasets  methods 
[8] base    

other attached packages:
[1] Biobase_2.1.7

loaded via a namespace (and not attached):
[1] affyio_1.9.1

Any idea how to resolve this problem?
thanks,
Sebastien