You are using FTPS with IIS 7.5 on a Windows Server 2008R2 server, from a client machine you are able to connect to the FTPS site but can not upload any files. You encounter the issue described in this article https://support.microsoft.com/en-gb/help/2888853/fix-the-supplied-message-is-incomplete-error-when-you-use-an-ftps-clie
There is a hotfix to resolve this issue (KB2888853) however, the hotfix is not publicly available from Microsoft. You will need to contact Microsoft to obtain this.
Please note that you will need to reboot the server after installing this hotfix in order for the changes to apply.