This issue is caused by reference files that lack the Macintosh File Type meta-data that allows Mac software to determine what is and isn't an appropriate file. The files on the X-Rite server are correct, but sometimes reference file will lack the Mac meta-data when downloaded and/or e-mailed via a PC. Sometimes they become corrupted during download even on a Mac. Additionally, files from the Kodak FTP site (for Kodak branded targets) do not always contain this data.
We've had great success using freeware called TextWrangler* to correct this problem. Typically, the user will simply need to open the reference file in TextWrangler and then select "File" > "Save as" and save the file to the "IT8 Targets" folder.
Word or BBEdit have also worked well for some users. However, Apple's TextEdit will not correct the reference information.
If simply saving the reference file out of TextWrangler or other acceptable program fails to correct the issue, follow these instructions to correct the file:
*TextWrangler can be downloaded at: http://www.barebones.com/