The gwscat program won't load because it depends on ggbio, which has a loading problem:

Error : (converted from warning) replacing previous import 
'ggplot2::Position' by 'BiocGenerics::Position' when loading 'ggbio'

Error: package or namespace load failed for 'ggbio'

I am working with a Mac (El Capitan) under RStudio (but same problem exists in R's own console), R v. 3.3.1, Bioconductor 3.3 and freshly downloaded versions of gwascat and ggbio.

Is there a workaround? 

Thanks, Jim Hunter

I'll answer my own question, thanks to the ggbio maintainer. Watch out for any option in your .Rprofile (if you have it) or interactive that sets warning = 2. This will translate warnings into errors and stop you cold.