Fixing security holes sometimes causes problems in perfectly normal activities. That’s the case if you’re a macOS user who relied on a specific kind of login method for Windows and Windows Server file sharing before June 2019. Microsoft released a fix for NTLM, a technology for managed authentication and security that dates back over a decade in its first version.
Two critical bugs in NTLM required updates for a seemingly every version of Windows and Windows Server released for several years that incorporate NTLM. These necessary updates broke Mac-based login sessions using standard Windows file-sharing protocols long supported in macOS.
If you’re in that boat and receive an error that there was a problem connecting to the server, you can follow Apple, Microsoft, and third-party advice to re-connect.
In Yosemite (macOS 10.10) and later, connecting in the Finder by select Go > Connect to Server and entering
smb://plus the IP address or full name of the server. This will create an up-to-date SMB connection.
If you have Kerberos authentication available, switch to that method for logging in, but the server has to have a DNS name and that name must be used instead of an IP address on the local network.
Apple also suggests that a Windows Server system administrator can enable “server message block (SMB) signing,” which reduces performance, but allows backwards-compatible connections from older Macs.
Ask Mac 911
We’ve compiled a list of the questions we get asked most frequently along with answers and links to columns: read our super FAQ to see if your question is covered. If not, we’re always looking for new problems to solve! Email yours to email@example.com including screen captures as appropriate, and whether you want your full name used. Every question won’t be answered, we don’t reply to email, and we cannot provide direct troubleshooting advice.