The error comes from the server. Though it can be some sort of incompatibility. The server seems to be Microsoft IIS. Do you know what version? Also, did you try to upgrade WinSCP? You should in any case. WinSCP 5.5 is almost 8 years old!
Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
Copying files to remote side failed - The specified data could not be decrypted