When you try to import an AIFF file that contains compressed data (known as AIFF-C) into Logic Pro or Logic Express, you may find that you are unable to do this. Instead, you will see this message:
"What kind of file is this?"
For AIFF files, this issue affects only Logic Pro and Logic Express 7.0 to 7.0.1. (See Getting the Logic 7.1 Upgrade).
This affects AAC and MP3 files only on Mac OS X 10.4 or later systems with Logic Pro or Express 7.1. The first time you try to import a file, the attempt may fail without any warning. On a subsequent attempt, you see the message ""xxx.aif - what kind of file is this?", where xxx is the name of the file.
When importing a compressed file, Logic starts by making an AIFF copy. The root issue is that these AIFF copies are sometimes left incomplete during the import attempt. On the second attempt, Logic attempts to reference the incomplete AIFF file rather than the original source file, which is why you see the message only on subsequent attempts.
To resolve this issue, update to Logic Pro or Express version 7.1.1 or later, available at Apple Downloads.