[R] Regarding error in RStudio

[Ivan Krylov]

Sounds like something weird happened to your installation of the knitr package. It could help to reinstall it. If you don't have anything valuable saved in %userprofile%\.RData, it may be worth moving it away, because it may be carrying a part of the broken state. (Saving state in .RData may be convenient, but it may hurt the reproducibility of your scripts and persist some of your problems.)
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Best regards,
Ivan