No, I haven't seen this before. From the description it sounds like a warning about very deeply nested elements. If I had to guess, I'd say it could be something to do with script code that generates markup, and is getting in some kind of bad loop where it just keeps inserting elements recursively until it gets so deep it can't keep track any more.
What's the context in which the error appears? When you open a document? When you perform a particular operation on a document? Something else?
It appears when we do a completeness check an is in the context of an informal table. The table is not that big, nor is it nested. It follows a graphic, I believe in a data module.
Hmm. I'm not sure then. Are you using the full Arbortext A&D solution, or just some S1000D doctypes with another CSDB system?
You might try grepping the code in your custom directory (and/or Editor install directory) for "tag level limit" and see if it turns up any hits. If you find the message, you might be able to get a better hint of what's happening by examining the code around it.
This was seen several years back when using multiple non-nested VERBATIM tags in a document.
The resolution was to
1) Make a backup of the file
2) Change the file from Read Only
3) Open ArbortextInstallPath\entities\ati-unc.dcl in an ascii editor
4) Find TAGLVL
5) Change the value from 48 to 100
6) Recompile the dtd
Issue was fixed in 5.4 M080.