Specified initialization vector (IV) does not match the block size for this algorithm

The problem is your initialization vector size needs to be 16 bytes.

Your initial vector size is 14 bytes.

You will need to increase the size of your initial vector by 2 bytes and your code will work.

Example:

string initVector = "HR$2pIjHR$2pIj12";

You will then get the output with your current code and the example IV (initialization vector) size provided:

hAC8hMf3N5Zb/DZhFKi6Sg==

This article provides a good explanation on what the initialization vector is.

http://en.wikipedia.org/wiki/Initialization_vector