Ok, so I fixed the path problem I noticed with logging last night. I suspect it's not the cause of your problem, so I've also attached an updated RTECompiler.class to do extra logging for _all_ of the flags we pass to the compiler, right before Live Errors performs the compile. So that should capture any problems with the classpath that might have been introduced on the Live Errors code path.
For the vsRTE.dll:
1) Exit SlickEdit if it is running.
2) Go to your SlickEdit install directory, go to the win directory, and rename/backup the existing vsRTE.dll
3) Copy in the vsRTE.dll that's attached to this post.
4) Restart. See if Live Errors still complains about your Log4j2 classes.
If it does still have problems:
1) Exit SlickEdit.
2) Go to the SlickEdit install directory, and from there go to the toolconfig\rte directory. Rename/backup the existing RTECompiler.class, and then copy in the RTECompiler.class that's attached to this post.
3) Restart SlickEdit.
Now, whenever Live Errors is triggered by an edit, the full set of compiler flags will be appended to %TEMP%\CompilerFlags.txt. There will be one argument per line.
I'd look at that first and check to see if the log4j2 entries are correct, and there aren't any mangled paths or odd looking compiler flags being sent. (note: the options in the file will not include the path to the source file of the buffer it's doing a check on, like you would do running a "javac" from the command line. We pass the buffer contents directly into the compiler API, so it doesn't appear with the other options).
Hopefully, that shows something wrong, because the alternatives are probably going to be harder to track down. Let me know what you see, and we'll go from there.