Problem with external dll

Hi guys, i'm newby on nsis programming.
i'm trying to call a method of dll from nsis using system plugin but i always get a chaine of char 'error' like value in the register of the result.
check is the name of dll

Code:
System::Call 'check::Sum(i, i) i (R0, R1) .R3'

and the prototype of function Sum is
int Sum(int s1, int s2)

i'm using the function Sum just to try if system:call works..

what's wrong in my code???
May someone help me????
thks

Use http://www.dependencywalker.com/ and make sure the exported function name is not decorated.

If the function is cdecl and not stdcall then you need to to use a switch, check the system readme.

Is this dll in the path so it can be found by LoadLibrary?

The libray is found by the progam.
I find the problem. VS2008 has created the library with non solved dipendecies, so i can't call correctly the functions in the dll.
Now i have another problem:
when i call the method of dll with systrem:call and i use .rX or .s the program rise a runtime error and stop working.
Why i have an error using . before registry or stack?
Have you any idea about this stuff?
tnk

.rX means no input, so if you have MyFunc(char*foo) then foo will be 0 and not a string in your function. It is generally used like this: For void GetNumber(int*num){*num=666;} you would use System::Call "dll::GetNumber(*i.r0)"