The function mentioned above isn't implemented in Qt/Symbian, which causes the assertion fail.
The previous comment is a very minimal implementation that is not correct.
The actual implementation needs to have some relation to the keyboard layout (for example on N97 keyboard the number keys are shared with letter keys)
IIRC, this function is supposed to do things like "CTRL + *" and "CTRL + SHIFT + 8" being equivalent on a UK querty keyboard. (on a Norwegian keyboard, it would be "CTRL + SHIFT + '"
I don't remember the details though.
My recommendation would be to do a default implementation for unknown keyboard layouts, and possibly do special cases for N97 / N97 mini and other devices that have alphanumeric keyboards, if needed.
HAL can be used to find out what device you are running on.
If the keyboard layout is localised (in a way that alters symbol placement) I don't know how to find that out