Updated question with more details:
I am not able to open my R workspace, and getting the following error (in base R, RStudio simply shows the first line of error and then freezes):
Error: value of 'SET_ATTRIB' must be a pairlist or NULL, not a 'list'
During startup - Warning message:
unable to restore saved data in C:\R_Library\A\.RData
Try renaming the file .RData in your R working directory. Start R, and run
load("whatever you renamed .RData to").
If this still does not work, try clicking on your renamed R project file. It should open your workspace with an empty environment.