I have a really vague problem, but I hope someone can help with it. I was modifying a C++ project and yesterday it was still working, but today it's not. I'm pretty sure I didn't change anything, but to be completely sure I checked the project out from SVN again and I even reverted to a previous system restore point (because this is a work computer, it sometimes secretly installs updates etc.). After succesfully compiling it, the program can start up, but after I interact with it, I get this error:
**The procedure entry point ?methodName@className@@UAEXXZ could not be located in the dynamic link library libName.dll.**

I've searched the internet, but most people's problems seem to be caused by an older version of the DLL being used. I searched my computer and there is no older version. If I delete the correct version, the application doesn't start. If I then recompile the project, the DLL is created again, so I'm both pretty sure that the application is using the correct DLL and that the compilation is creating it. If I introduce syntax errors into the method that the error refers to, the project refuses to compile, so I guess this means that it is also compiling the files that contain the method.

Basically I don't know anything about DLL's, linking, etc. so I would greatly appreciate it if anybody has an idea as to why the functions that are very clearly defined in the project are all of a sudden not making it into the DLL anymore. I know this is vague and if any more information is required I will gladly provide it. Thanks!

**Update:** I have tried the given suggestions, but I'm still stuck. `__declspec(dllexport)` is apparently not used in the entire project. Opening the DLL with Dependency Walker shows me an empty top right section and the section below it lists the function from the error message. If I check *Undecorate C++ Functions* it looks fine, but if I don't I get the weird question marks and @s from the error message and there appears to be a difference at the end:

```
?methodName@className@@UAEXXZ
?methodName@className@@UAEXH@Z

```

Perhaps this is the problem, but I have no idea what it means, what may have caused this and what I can do about it.