Circos could not find the configuration file [%s]. To run Circos, you need to specify this file using the -conf flag. The configuration file contains all the parameters that define the image, including input files, image size, formatting, etc. 

If you do not use the -conf flag, Circos will attempt to look for a file circos.conf in several reasonable places such as . etc/ ../etc 

To see where Circos looks for the file, use

  circos -debug_flag io

To see how configuration files work, create the example image, whose configuration and data are found in example/. From the Circos distribution directory,
	  
  cd example
  ../bin/circos -conf ./circos.conf

or use the 'run' script (UNIX only).

Configuration files are described here

  http://circos.ca/tutorials/lessons/configuration/configuration_files/
	  
and the use of command-line flags, such as -conf, is described here

  http://circos.ca/tutorials/lessons/configuration/runtime_parameters/

Windows users unfamiliar with Perl should read 

  http://circos.ca/tutorials/lessons/configuration/unix_vs_windows/

This error can also be produced if supporting configuration files, such as track defaults, cannot be read.