We have identified an issue with MacOS High Sierra (10.13) which can cause uploads to fail when using CtrlPrint. Our development team is currently investigating the issue. If you are experiencing issues make sure that you are using the most recently released version of Transfer Manager (1.2.1) which includes a fix to help avoid this problem.
At this time we recommend that users do not upgrade if possible to the latest MacOS to avoid potential problems.
For users who have already upgraded, the current solution to the problem is to simply retry the failed upload again (you will find the file listed in the "Open recent" option under the "File" menu.)
We appreciate your patience while we work on this. Please feel free to contact us with any questions you might have.