Issue with R6: error message says: there is no package called 'R6'

[nszekeres]

Hello, trying to "preview" a document in markdown, and keep getting this issue:

Error in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]) : there is no package called 'R6' Calls: <Anonymous> ... loadNamespace -> withRestarts -> withOneRestart -> doWithOneRestart Execution halted

Any ideas on how to resolve? FYI, I removed R and Markdown and reinstalled... it told me "success" but is still not allowing me to preview a document in html or word.