Since I moved to R 4.0.0 and Rtools 4.0 I get the error message in the subject line when I start a new Git bash terminal. The error message continues:
This problem is probably due to using incompatible versions of the cygwin D
LL.Search for cygwin1.dll using the Windows Start->Find/Search facility
and delete all but the most recent version. The most recent version shoul
reside in x:\cygwin\bin, where 'x' is the drive on which you have
installed the cygwin distribution. Rebooting is also suggested if you
are unable to find another cygwin DLL.
I only have one cygsin installation, although it is located in c:\cygwin64 rather than c:\cygwin. So far it hasn't actually stopped me from doing anything in the terminal, so maybe it doesn't matter, but it would be good to know how to fix it if anyone can help.