CSV import plugin issue

By design9 - April 25, 2013

We recently upgraded the CMS on two of our sites to v 2.51. We had these upgraded through some customization work we had done as well. When I now try to use the CSV plugin, I am getting the following error message: 

Please upgrade the admin.php file, it is out of date!

Can you tell me how to fix this because I need to use the CSV import before our April 29 deadline for our magazine.

Thanks!

April