The issue is likely that you are using xtable 1.8-6, and the current version on CRAN is 1.8-4. The package sources section of the shinyapps.io user guide CRAN, GitHub and BioConductor are supported as sources of packages but R-Forge (which is where I found xtable 1.8-6) is not. If your app will work with 1.8-4, you might try downgrading to that version.