Unresolved external

[ILINK32 Error] Error: Unresolved external 'Proc_msi60541(long double, long double)' referenced from C:\CALC\DEBUG\UNIT1.OBJ

[ILINK32 Error] Error: Unable to perform link

#include "msi60541.h"
...............много строчек кода...............
    case 14:
            r=StrToFloat(Form1->Edit1->Text);
            Edit1->Text="";
            Label3->Caption="function";
            a7=1;
            break;
...............много строчек кода...............
if (a7==1) {                     
            w=StrToFloat(Form1->Edit1->Text);
            y=Proc_msi60541(r, w);
            Form1->Edit1->Text=FloatToStr(y);
        }

#ifdef BUILDING_MSI60541_DLL
    #define TYPE_MSI60541 __declspec(dllexport)
#else
    #define TYPE_MSI60541 __declspec(dllimport)
#endif
 
TYPE_MSI60541 long double Proc_msi60541(long double, long double);

#pragma argsused
long double Proc_msi60541(long double r, long double w)
{
    long double y=(r/2)*tan(w/2);
    return y;
}
int WINAPI DllEntryPoint(HINSTANCE hinst, unsigned long reason, void* lpReserved)
{
    return 1;
}