Error in drupal "Notice: Undefined index: extension in require()..." I am seeing this error on my page 


  Notice: Undefined index: extension in require() (line 207 of
  /home/....../public_html/includes/filetransfer/sftp.inc).


I have no idea from where. I tried doing search but I did not see any help.
Could you please guide why this message is poping up on all the pages.
There is not an sftp.inc in the filetransfer folder in Drupal core by default. Perhaps more information on your contributed modules in use, a custom module, Drupal version, etc. might help...