I have encountered several .mi files that have contained corrupted characters in them.

When you try to render, Iray produces and error (thankfully) that indicate the line number containing the error, so it is possible to manually fix the problem and attempt to render again.

OBSERVATIONS:
1) This is not consistent. If you encounter a corrupt file, and do the same export again, even in the very same iClone session, the next export is likely to be clean.
2) It seems more likely to happen on larger files. I don't know if the size "causes" the corruption, or if it merely a matter of statistical odds, meaning if the error is one in 50 million characters, you are more likely to have a problem in a 20-million character file than a 1-million character file.
3) So far I have only seen the problem in the .mi files, not any in the .shader_decl.mi files.
4) It is not my disk drive. I have exported to a different hard disk drive, and gotten errors there too, and neither risk reports any errors, so I think that eliminates my disk drive as being the culprit. Also, I've seen it on both my Win7 desktop and my Win10 laptop.
5) I have has as many as 3, maybe up to 4, errors in a single file, but usually only one.
6) I estimate it is happening on about 5% of my big-project exports, roughly. Not pervasive, but more than enough to be a serious problem.

The following pictures give examples of the errors I'm getting. The last picture is an example of the error message.


P.S.
This was discovered in the "beta 2" version. I have not yet had an opportunity to verify it on the "beta 3" build, but I needed to be sure it got reported. If this was a "known problem" that was not reported to us, but has been fixed, please let me know. Otherwise the only way for me to know it had been fixed is by going a long time without seeing the error. Or I'll encounter it, and then I'll know it has not been fixed.

P.P.S
If anyone thinks I'm exaggerating about the number of characters in "Observation #2" above, the "Drive-In Theater" scene generates a .mi file consisting of 7,013,128 lines of text and 413,498,510 ASCII characters.