If you get the message " INTERNAL ERROR " in your log files, it means that Samba got an unexpected signal while running. It is probably a segmentation fault and almost certainly means a bug in Samba (unless you have faulty hardware or system software).
If the message came from smbd, it will probably be accompanied by a message that details the last SMB message received by smbd. This information is often useful in tracking down the problem so please include it in your bug report.
You should also detail how to reproduce the problem, if possible. Please make this reasonably detailed.
You may also find that a core file appeared in a corefiles subdirectory of the directory where you keep your Samba log files. This file is the most useful tool for tracking down the bug. To use it, you do this:
$ gdb smbd core
adding appropriate paths to smbd and core so gdb can find them. If you do not have gdb, try dbx . Then within the debugger, use the command where to give a stack trace of where the problem occurred. Include this in your report.
If you know any assembly language, do a disass of the routine where the problem occurred (if its in a library routine, then disassemble the routine that called it) and try to work out exactly where the problem is by looking at the surrounding code. Even if you do not know assembly, including this information in the bug report can be useful.