1756-L37 and USB. Trouble connecting

For the first time, I'm using a AB processor with a serial port. All worked well, and I was able to flash it over USB, but eventually, I started doing my regular work over the ethernet port (ENBT card), since I was most familiar with it. Now, that card is being used by a dedicated ethernet for FlexIO, and I assumed I could go to the USB port for programming.

That doesn't appear to be the case.

Even though I can see the USB connection in RSWho, and browse the whole rack, I cannot "Go Online", without a "Failed to go online with the controller. Unable to open connection - all connections my be in use" error.

Am I doing something wrong?

The key is in the error message "All connections may be in use".

The controller will have a fixed number of connections for communications, your IO takes up connections, communications to other HMIs or PLCs can take up connections...you could be at the limit. Especially if you have a lot of analog cards in your system as each analog card can take up a single connection. You'll have to give more specifics of your system for use to better investigate.

But, if you can shut down an HMI then try to go online. If you can get online after that you have to many things trying to communicate. You may need another control network to break up the load.

If i was out of connections, I would expect that by stopping using the ethernet connection for programming, that it'd free up the "connection" for USB.

Interesting point, though. Maybe I made a mistake in re-ethernetting the FlexIO drops. Maybe I'll try unplugging some ethernet cables...

Oh, so, I have a L73, with ENBT, a Prosoft card (disbaled), a AIM, 5 DIMs, and 3 DOMs.
At the other end of the ENBT are two FlexIOs, each with 1 AIM, 3 DIMs and 1 DOM. The HMI is offline.

The 1756-L73 supports 500 CIP connections, so you haven't actually run out of Connections. There's something munged up in the driver or the way the controller is calculating connections.

Do the usual troubleshooting steps; shut down RSLinx Classic, delete the Harmony.RSH and Harmon.HRC files, reboot the PC.

Since this is a system startup I presume you'll have an opportunity to power-cycle the controller.

I shut down RSLinx, renamed those two Harmony files, rebooted. The PLC was also off (for all night).

Same message. And, it (of course) recreated the Harmony files.

I may have to drop back to ethernet for development, at least for today.

Issue ""Failed to go online with the controller. Unable to open connection - all connections my be in use" error."

Solution: The IO in CPU might have been corrupted so try by switching OFF the controller, remove the battery and insert the battery available in Left side of the controller.

Sebastian C