Can't Join Tracks??

What does it mean if I can't join two sections of track? I can join them by placing a separate short section between them.
These are the SAP TRS19 132lb series. I have had this before over several years. Normally I just stick in a new short section
and move on. However, this time during a RUNAROUND the train refuses to enter the "repair".
Note: many miles away there are two trains on-track.

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I just kept deleting sections of track until I found one that would accept a Join. This has been around
for a long time, at least in my experience.

I had that once and it turned out my track had somehow turned into a fixed track-type object. I could click and rotate it in the scenery objects and everything. I deleted the track and laid it down again without any issues. I even tried a DBR, but that didn't fix that problem.

Deleted and relayed. All ok now (should say for now).