What is a stack overflow error?
Parameters and local variables are allocated on the stack (with reference types the object lives on the heap and a variable references that object). The stack typically lives at the upper end of your address space and as it is used up it heads towards the bottom of the address space (i.e. towards zero).
Your process also has a heap, which lives at the bottom end of your process. As you allocate memory this heap can grow towards the upper end of your address space. As you can see, there is the potential for the heap to "collide" with the stack (a bit like tectonic plates!!!).
The common cause for a stack overflow is a bad recursive call. Typically this is caused when your recursive functions doesn't have the correct termination condition, so it ends up calling itself forever. However, with GUI programming it's possible to generate indirect recursion. For example, your app may be handling paint messages and whilst processing them it may call a function that causes the system to send another paint message. Here you've not explicitly called yourself, but the OS/VM has done it for you.
To deal with them you'll need to examine your code. If you've got functions that call themselves then check that you've got a terminating condition. If you have then check than when calling the function you have at least modified one of the arguments, otherwise there'll be no visible change for the recursively called function and the terminating condition is useless.