An AI file is a file of the vector based drawing program Adobe Illustrator. The AI format is a proprietary format containing one-sided vector drawings stored in either EPS or PDF format.
In addition to Adobe Illustrator, there are also a number of commercial and freeware drawing programs that can import or import AI files. However, since Adobe further develops the AI format, it can happen that with foreign software AI files that were created with a newer Illustrator version (CS3, CS4, CS5) can not easily import.
Remedy here either only the most recent version or the file in the Illustrator as a compatible version to save (just save when saving an older Illustratorversion)