Hi Andrew,
This works perfectly with regard to how it used to work. I don't put the extension on and it does save it as an SEQ WITH the extension appended. No errors; with the SEQ saved on the same drive as the RealBand folder the RBBackup folder in the RealBand folder gets all the backups sequentially to the limit allowed and the oldest file flushed to Recycle.
Saving on another drive does the same but the backups are stored on a local RBBackup folder at the root of that drive.

I now go back to my original song and load the SGU file as created by BB. Generate all the tracks and then click Save. I navigate to the folder where I saved that previous successful file. I don't enter an extension so I am asked for Melody and Soloist details and I click OK and it saves as an SGU, despite the fact that the dialog says saving as type SEQ.

I go back and save again, but this time I append the SEQ extension and it works just fine.

Back to RealBand and one more save, this also works fine

Another save and I get the error and the TMP will not overwrite the SEQ.

The first SEQ save didn't backup the SEQ because there was nothing to back up

The second save made a backup in RBBackup and replaced the SEQ file with the TMP

The third save tried to backup the old SEQ but for some reason couldn't and so would not replace the SEQ file with the temp.

So what is the difference between these two types?