The error message “Failed to synchronize Resources folder” may occur when trying to make a new client-server connection, especially if the connection is cross-platform (e.g. 4D Remote on Windows connecting to 4D Server on Mac). This error might be accompanied by "Error code: -10517". Usually, this synchronization error is due to certain files in the Resources folder having filenames that contain characters that are not cross-platform friendly, such as backslash (“\”) or colon (“:”). To avoid this error, either remove the offending files from the Resources folder, or modify the non-cross-platform characters in the filenames.