The Monster plugin was compiled using an older version of gcc (2.91.66 or egcs-1.1.2).
Newer versions of gcc will complain about the SetUse(), SetThink() and SetTouch() calls. If there was this in the source code...
SetUse(MyUseFunction);
...it would need to be replaced with...
SetUse(&MyClass::MyUseFunction);
You will have to go through the source code and change all of these to match this format.
I have made similar changes to the SDK 2.2 source code found on my website. Download the SDK 2.2 patches shown here...
http://hpb-bot.bots-united.com/building.html
and either look at the diff files or run the batch file that converts the original SDK 2.2 source code, then compare the original SDK 2.2 source code files to those patched files to see what needs to change for a newer version of the gcc compiler.
It's a LOT of changes and if you aren't very familiar with C++, you WILL have problems converting things. So if you aren't good with C++, be prepared for some trouble.
botman