We should probably all apologise (mostly myself) for derailing your thread - your answer is way back in post #2 by dmargineau. The software version is the issue.
I suspect you may be new to Logix-platform PLC's and software, so here's a quick primer to help you understand
why.
RSLogix 5000 is a software package that was released to program Logix-class PLC's. There were several versions of this software released, the latest being v20. There will be no more (major) revisions of this software package released, as it has been superseded by...
Studio 5000 is a suite of software packages, including
Logix Designer and
View Designer. Note the distinction here -
Studio 5000 is the "container", if you like, that holds multiple software packages, not the software package itself. The software package that you're interested in, which is contained within the Studio 5000 suite is...
Logix Designer is for all intents and purposes a re-branded
RSLogix 5000. It is used to program Logix-class PLC's. The first version of this software is v21, and at the time of writing, the latest version is v30.
Now, here's the "quirk" that's catching you out (I think).
All PLC's run firmware, and Logix PLC's are no exception. But to program a Logix PLC,
your software version must match the PLC's firmware revision.
So, if your PLC has firmware version 16, you will need
RSLogix v16 to program it.
If your PLC has firmware revision 24, you will need
Logix Designer v24, which comes as part of the
Studio 5000 v24 package, to program it.
If you have PLC's with 10 different firmware revisions, you need the same 10 software versions on your PC to program them. The good news is that you can have as many versions of RSLogix 5000/Studio 5000/Logix Designer installed on your PC as you want - they all run simultaneously side-by-side. If you double-click on a v16 project, RSLogix v16 will open. If you double-click on a v29 project, Logix Designer v29 will open. the additional good news is that your license - as dmargineau explained in post #4 - is not version-specific. If you have a license for one version of RSLogix 5000/Studio 5000, you can run them all.
Now, as to the "kerfluffle"...
You only need to match
major firmware revisions, to make everything work. You can program a PLC with firmware version 29.99 using Logix Designer v29.00, or vice versa (those actual minor revisions don't exist, but you get the idea). No problems. Except...
RSLogix 5000 v20.01 was released.
Logix Designer v21.01 was released.
No problems so far...
RSLogix 5000 v20.03 was released
Logix designer v21.03 was released
And for the first time, the minor revisions were
incompatible. So, if you programmed a PLC with v20.03, someone using v20.01 could no longer go online with that PLC. And,
you can't install two copies of the same major revision on the same PC. So, you can either have v20.01 or v20.03, but not both, and if your PLC was programmed with the version you don't have, you're in a pickle. The same was true of v21.01 and v21.03.
To rectify this, Rockwell released RSLogix 5000 v20.04, which plays nice with both v20.01 and v20.03 PLC's. If you install RSLogix 5000 v20.04, you will not have this minor revision issue and you can get back to more important things, like wondering who first came up with the term "kerfluffle".
Rockwell did not release a fix for the v21.01/v21.03 "kerfluffle", other than (as I mentioned above) releasing Logix Designer v23, and telling everyone to just update any PLC's currently running firmware revision 21, to firmware revision 23.
So, circling back around to why all of this is important...
The 1769-L23 is an older-series PLC, and the newest firmware revision that it supports is v20. If you want to work with it in it's current form, you will need to find out what revision of firmware it currently has, and acquire a copy of RSLogix 5000 with a major revision to match (again, your existing license will still work, you just need the software). Or, if you just want to create a new project and start from scratch, you can pick whatever version of firmware you want, and just flash the L23's firmware to suit. But,
the 1769-L23 cannot be flashed any higher than v20.
If you're using the L23 in a new application, you'd be best to flash it up to the latest possible version of firmware (v20). But if you do, take heed of the "kerfluffle", and make sure to install v20.04 of RSLogix, not v20.01 or v20.03.
Clear as mud?
As to your specific problem: Logix Designer starts at v21, and the 1769-L23 can only be flashed as high as v20.
That's the heart of your issue. Logix designer doesn't know about the L23, because no version of it has ever supported it. You need a copy of RSLogix 5000, just to so much as "choose" that PLC. And then, of course, you need the
right (or rather,
matching) version of RSLogix 5000, to actually work with it.
Edit: if you want the TL;DR version, just re-read dmargineau's post #2
