When you see this error, the names of the file (or some of the files) you are copying is too long.
How to solve this?
When using Windows Explorer, you can shorten the name of the file you are copying and then try to repeat the process. You can also access the vault through a third party WebDAV client and work with the files with the long names flawlessly.
Why we can’t we solve this
This problem does not occur in Cryptomator but actually in Windows Explorer. When this happens, the Cryptomator application does not even know that an attempt to copy a file has been made. Thus, we currently have no direct influence on the behavior or error message.