A firewall or antivirus (like Bitdefender) might be standing in the way, mistakenly flagging the Remote Desktop request as a threat and cutting the line instantly.
Combined, these codes signal that the client cannot reach the target machine because the communication path—often managed by a gateway or firewall—has been severed or blocked. ⚡ Common Causes
The most common cause of this error on Windows Servers or Azure VMs is an expired self-signed certificate. A firewall or antivirus (like Bitdefender) might be
If fragmentation is suspected, reduce the MTU by typing: netsh interface ipv4 set subinterface "Ethernet" mtu=1400 store=persistent (replace "Ethernet" with your actual network adapter name). 4. Update the Remote Desktop Client
Click , browse to C:\Windows\System32\mstsc.exe , and add it. If fragmentation is suspected, reduce the MTU by
Open .
Run: REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server" /v MaxOutstandingConnections /t REG_DWORD /d 65536 . the computer. 5. Adjust Security Layers (Legacy Support) right-click your valid RDP certificate. "Fine
REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server" /v MaxOutstandingConnections /t REG_DWORD /d 65536 your computer. Microsoft Learn disable Network Level Authentication (NLA) as a temporary security workaround to test the connection? Fix Remote Desktop Error Code 0x904: 4 Working Solutions
If a certificate renewal occurred but the Remote Desktop service cannot read the private key, the TLS tunnel will fail immediately. Inside certlm.msc , right-click your valid RDP certificate.
"Fine," Aris muttered, rubbing his eyes. "A hiccup."