Getting XMLRPC Error when using external writing software

Hi everybody!
I’m experiencing some strange behavior with the XMLRPC connection (both with WP4.0 as well as 3.9.2). I have two external editors on my mac. One is “Marsedit” the other is “Blogo”.
Whereas Marsedit manages to connect via XMLRPC without any problem the other, Blogo, returns an error “something went wrong with the XML-RPC connection”. Now, their support has not yet found a solution and I’m just a user not knowing anything about PHP. I can, however, change some files if this would be necessary via FTP and such. Just not knowing what I’m doing 😉

I’ve also already tested each and every plugin running, deactivated and reactivated each plugin to see if it worked then – no success.

Does anybody here have any suggestion what to do? My blog is rather old (www.macmaniacs.at) and so is it’s database. I’ve had some troubles with the database years ago but recently it worked really well.

Any suggestions more than welcome!

cheers,
Holger