Preview not showing up during RAW import

Question

So I want to import some pics and this statement comes up, " Preview unavailable for this file" see attached. I imported the pics once and then realized that I did not batch name them like I always do. So I deleted them from LR then renamed them in Bridge, then tried to important them again, it is a no go. So I have LR 4.1, I use Mac book pro, Mac os x version 10.7.4. attached is a screen shot. Ok also I am pulling these pics off of my external Hard drive, I have never run into this problem before when I was using LR3.

Answer 1

I can't think of many situations where a colon (:) is not a reserved character - so, unwise inside a filename - at least, in the MS Windows context.
I understand MacOS may have looser rules in its own right, and one may seem to get away with all kinds of things. But it seems to me a bad idea to flirt with incompatibility where you don't have to - remembering that with LR it is particularly easy to switch platform due to the licensing arrangements. Such an application is likely to be written so as to work as smoothly as possible across both; which requires, so as to conform to the rules of both.
Other sometimes problematic characters include < > \ / | , much punctuation including ! ?, @, probably others too.  Some such as the semicolon (;) may be perfectly fine in many contexts, but prove unsuitable for others - for example, they may breach the file naming rules of a CD's or DVD's file system.
I encountered a problem recently archiving several thousands of someone else's files, where anything with a semicolon in the name was rejected by the software involved. It was impossible to search and replace semicolons with a more acceptable character - because a semicolon was flagged as invalid entry by the search dialog. It took me several eye-crossing hours to track down and fix every single one by hand. Word to the wise.
Personally, I stick habitually to alphanumeric, international accented characters etc, space, square and round brackets, hyphen and underscore - avoiding all other punctuation marks except for the dot immediately before the file extension. It may be a little more restrictive, but it is a lot more certain.