try catch not getting hit on external ipaddress

On my site I have several functions which have a try catch in and the start of the try I pass a got into message into the database I then have the code needed in the function and then in the catch (Exception ex) I pass the error into the database. This works fine when running it on the company network internally but when ever I try a different network with an outside IP address that all the users will be using it stamps the first got into message into the database but not the catch error message.
I know this isn't stamping the error into the database and not just not erroring because I have tested the code passing in an invalid date 31/09/1984 I have also tried removing the Exception ex and passing in a simple string value to the database instead of the exception message but this still isn't getting recorded. 
I am thinking the catch is never getting hit but can't work out why as it is from the internal site can any one help and give me any ideas let ...