You're using a very old version of Chilkat from 2011. Update to the latest to see if the problem is already resolved.
In general, protocols such as TLS, SSH, etc. will evolve over the years to newer protocol versions, newer algorithms, etc. Servers will begin disallowing what was previously secure in past years, but is no longer secure. It is not a valid expectation that software (never updated), will continue to work when interacting with servers that are updated from time to time. The current version of Chilkat (or anything else) in 2018 will surely not work with whatever exists in 2028, which hasn't yet been invented.
My recommendation is to avoid being too many years out-of-date. If you are using something quite old, such as in this case, it is overwhelmingly likely that updating to the latest version will fix the problem.
