I am using RSLogix 500 v 7.10.00

The issue is that the "next unused" feature of the address wizard is perfectly working until I use indirect address for the first time. After that it stops functioning for good.
Two screenshots illustrate the problem.
Actually, the "next unused" feature stops working already during the typing of the indirect address, after the first [
Any ideas?
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I was able to duplicate your problem. However, if you create a new binary file B:9 for instance, then the next unused works. I believe it is because of the B3:[N7:0]/[N7:1]. With this "double" indirect addressing, there is no way for the software to know what the next unused element is. Because B3:[N7:0]/[N7:1] could be any bit in the entire file.

Thanks a lot!
You are right. I never thought in such aspect.
Unfortunately, this leaves me without the tool, since the idea is exactly to access whatever bit in entire B file.

Just a thought while you are writing your program. If B3:[N7:0]/[N7:1] is the only index of B3 like this replace it with B9:[N7:0]/[N7:1] or some other unused data file. Write your program with will allow you to use the next unused address, then when you are done put B3:[N7:0]/[N7:1] back in place of B9:[N7:0]/[N7:1].

That would get you through until you are ready for your first online test. Kind of a pain but...

On a tangent.

Why the blue background, reminds me of the old DOS programs. When you go on line, what color are the true instructions?

Just like this color combination (Mitsubishi Medoc for DOS is my first love ).
True conditions are green.