cder'' returns information about a cd domain error:
0 0 - no error
1 0 - file not found
2 0 - procedure not found
3 0 - too many DLLs loaded (max 20)
4 0 - parameter count doesn't match declarations
5 x - declaration x invalid
6 x - parameter x type doesn't match declaration
cderx'' returns GetLastError and text from the last cd.