Click on the DOpus icon and then choose Icons/Information from the menus. You should get a window that shows all sorts of lovely stuff, with Tooltypes and things. One of the things is the Stack size - you can change it in there too.
The Stack is an analogue of the spike on a stand that people used to have on their desks (if you're old enough to remember such a thing) onto which you push bits of paper that have to be dealt with. You can then pull things back off the spike (stack) when you want/need to deal with them. It is a FILO (First In Last Out) buffer that provides some temporary storage for a task.
You might also have seen such a thing in a restaurant or cafeteria - the thing that has a spring-loaded stack of plates in a cylindrical holder. Clearly you cannot get at the first plate that went in until you have removed all the other plates from the top first.
Stack usage consists of "Push"ing things onto the stack, and then "Pop"ping (or pulling) them off again.
Another common type of buffer is FIFO (First In First Out) which can be used in pipes, disk buffers, stream buffers, and so on.
If the Stack is too small then the program will run out of temporary work space for some functions, and you will get problems. Try increasing the amount shown in the Information window by entering a bigger number, say 32000 (bytes), 48000, 64000, or something, and pressing Return and then click on Save. If the problem is Stack related then eventually it will go away once the stack is big enough.
Edit: comment out or remove your user-startup entries first. Icon Information entries will take priority anyway.
I usually ran my DOpus on a separate custom screen, because it's better that way, and did not iconify it at all, but did *sometimes* pop it onto the Workbench screen - mostly because I could. (Mind you, I also ran MCP.)
