Hi Kris,
You could try increasing the memory as jmr suggests. You can increase it to way more than 64MB if you need to so you can experiment and see if it makes a difference.
However if you are getting a 500 error, that definitely points to the server. Your hosting company should be able to help you find a log entry that tells you what caused the 500 error.
500 is not a really specific error message, it mostly indicates that the server tried to access something that wasn't available. Most of the time it's permissions or a transient server error.
Contact your host and see if they can help pinpoint the cause of the message.
Ed