I instantiated an entity from an External Library like so:

...
 
U_S2P : entity util.serial2parallel(rtl)
generic map (WIDTH => 2)
port map (clk, rst, din, din_v, dout, dout_v);
 
...

And an error marker appeared next to the first line shown above saying "Undefined architecture rtl". The real problem is that the source file in the util library called "serial2parallel" had a code error, and failed compilation. But since it is external, a confusing error message was given.

At the very least, an error message saying "External Library util contains errors" as a marker in any file that tries to import the error-containing library would be good....better would be if the marker said "util.serial2parallel contains errors".