How to track down Rstudio "access is denied" errors?

[fango]

I need help in tracking the source of RStudio error messages most likely related to access issues on Windows 8.1.

Description
At start-up and while executing scripts repeated errors such as

Error in normalizePath(path.expand(path), winslash, mustWork) :
path[1]="C:/Users/Fango/AppData/Local/Temp/RtmpGaeqZ9/rstudio-available-packages-6e0045d14ef": Access is denied

appear in the console.

1. The respective directory does exist and user "Fango" has all access rights. No other users have rights except "SYSTEM"
2. Scripts do run and seem to work as expected.
3. Those messages appear typically at start up, when saving script after editing but also in between.
4. No such issues/messages when running scripts from the plain R console (i.e. without using RStudio).
5. No such issues when I start RStudio with administrator privileges

In addition I receive warning messages such as

Warning messages:
In drawGTree(x) : reached elapsed time limit

Again, I do not get those warnings when using the R console.

Versions:
RStudio Version 1.2.5033 ("Orange Blossom" (330255dd, 2019-12-04))

Windows 8.1 Version 6.3 build 9600

R version

platform i386-w64-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 3
minor 6.3
year 2020
month 02
day 29
svn rev 77875
language R
version.string R version 3.6.3 (2020-02-29)
nickname Holding the Windsock