Nomadesk is not able to synchronize duplicate files that have the same name but differ only in case.
Nomadesk for MacOS creates a Vault based on a case sensitive Filesystem that allows creation of duplicate files with a difference in case.
Example: A file called "My report.doc" exists on your Nomadesk Vault. You open the file for editing and save it as "my report.doc". Nomadesk detects this file and will alert you that this file cannot be synchronized.
Solution: Rename or remove the duplicate File from your Vault.