Error in readRDS(pfile) : unknown input format AND MORE

When starting Rstudio, I am getting:

Type 'q()' to quit R.
Error in readRDS(file) : unknown input format
Error in readRDS(file) : unknown input format
Error in readRDS(pfile) : unknown input format

Then,

> packrat::status()
Error in readRDS(pfile) : unknown input format
In addition: Warning messages:
1: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file11a432497fd7'
2: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file11a469e63773'
3: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file161041c23441'
4: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file161070ae55b4'
5: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file1610d3f36be'
> packrat::clean()
Error in readRDS(pfile) : unknown input format
> packrat::status()
Error in readRDS(pfile) : unknown input format
In addition: Warning messages:
1: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file11a432497fd7'
2: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file11a469e63773'
3: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file161041c23441'
4: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file161070ae55b4'
5: In FUN(X[[i]], ...) :
  No DESCRIPTION file for installed package 'file1610d3f36be'

This some of this for good measure,

> packrat::clean()
Error in readRDS(pfile) : unknown input format
Calls: <Anonymous> ... system.file -> find.package -> lapply -> FUN -> readRDS
> remove.packages("data.table")
Removing package from ‘C:/Users/rbruner/Dropbox/HIGHSCOPE/packrat/lib/x86_64-w64-mingw32/3.3.2’
(as ‘lib’ is unspecified)
Error in readRDS(pfile) : unknown input format
Calls: <Anonymous> -> .rs.listInstalledPackages
Error in remove.packages : Error in readRDS(pfile) : unknown input format
Calls: <Anonymous> -> .rs.listInstalledPackages

Basically, the whole packrat project seems to have gone AWAL. I am not sure what is going on, or how to recover it. All I know is that I came back after the weekend to find this.

Use the reported RStudio startup and packrat::status(), packrat::clean(), and remove.packages() calls as reproduction steps. Investigate the unknown input format error alongside the missing DESCRIPTION warnings; done means the cause is identified and the reported packrat operations complete without the error.