Getting all primes between 0 - n
Leaving aside the algorithm there are a number of points about the code

Naming
Pascal casing is standard for C# - SimplePrimer and FindVersion as opposed to simplePrimer and findVersion.
FindVersion seems unconnected to the functionality.

Structure
public fields are generally frowned upon.  If it needs to be part of the interface, make it a Property so that the implementation can be changed if needed.
Having a separate 'return' as PrimeList seems overly complicated. There is no strong reason for not having List&lt;BigInteger&gt; GetPrimes(BigInteger goal)
Looking at the code, I cannot see anything obvious that might throw an exception that might be caught by the catch (perhaps an out of range on the BigInteger?) Is it needed? 
As a shape I would push for any output to be external to the function. Have the calling code catch errors or report results. It makes unit testing a lot simpler