Hi Markus are you getting this error with or without the SSL configuration? Because in the error above it seems to be complaining about the SSL connection initialization together with issues in accessing subscribed_properties.bin file under the specified location. What sort of user are you working with?
I get this error by strictly adhering to the C SDK Quickstart guide. On the side note, the download link for C SDK provided in the guide does not contain the whole library and the files that are referred to in the guide.
I am trying to get this to work with SSL, but I have already tried to disable SSL as well, but weirdly and regardless, the "Error intializing SSL connection"-error persists.