To convert a CAESAR II file to 2011, 2013, 2014, 2016, or 2017 you have to perform a netural file conversion of the C2 file.  To perform this conversion follow the steps below.  

1. Open up your version of CAESAR.  

2. On the Interfaces tab, select CAESAR II Neutral File.

3. Click on (1) to choose to convert from a CAESAR II input file to a neutral file, and then click on (2) to browse to your file to convert.

4. Now, the file will be converted into a file with the same name, but with the extension *.cii.  The file will exist in the directory your previous file was in.  Select Convert.

5. After this conversion, Change your conversion type back to "Convert Neutral File to CAESAR II Input File", choose the neutral file you created in step 4, and create the C2 file.  This C2 file will be able to be opened by your current version of CAESAR.