Unable to open illustration due to a new version error

Hi guys,

I recieved an error message indicating can't open the illustration. The file was generated by a new version of illustrator and cannot be opened. Please ressave it in a format compatible with your version of Illustrator

for both the esp and ai files I recieved for two seperate projects.

The issue is I contacted the senders and they were indeed saved for older versions. One of the projects came with various files and all opened correctly, but one and no one else had any issues opening the file generating the error message.

Here are my details and what I'm using:

- CS5.1

- OSX 10.9 w/ 3.2 Ghz Intel Core & 16 GB memory

If anyone has any suggestions on fixing the issue your help would be greatly appreciated! I've tried opening in InDesign and exporting as well but no luck.

Thanks so much!