Correctly using DLLEXPORT and ALIAS

Hello, I am attempting to make use of a number of fortran functions and subroutines in a C++ project by using a generated .lib file. When compiling my C++ project, I get a linker error:

error LNK2019: unresolved external symbol _Leakage_SPH referenced in function

The function is called with Leakage_SPH (note no underscore), so I think this is the root of my problem. When I check the fortran code for this subroutine, I see:

Subroutine Leakage_SPH(Nu0,FracLkgTot,tlkg,NHoles,
     +                       ObjDat, holeAreas, holeHeights)

!DEC$ATTRIBUTES DLLEXPORT, C :: Leakage_SPH
!DEC$ATTRIBUTES ALIAS : '_Leakage_SPH' :: Leakage_SPH
!DEC$ATTRIBUTES REFERENCE :: FracLkgTot

This appears to give an alias of _Leakage_SPH so that the definition can be found. But something isn't working. The code compiles in fortran and the library is generated and placed in the correct spot. One thing I noticed is this remark that I get when compiling the fortran code:

remark #5082: Directive ignored - Syntax error, found ':' when expecting one of: , <END-OF-STATEMENT> ;

This appears to be pointing to my ALIAS line. Can anyone see what error I've made? Apologies if I've messed up any formatting; this is my first time posting on this forum (and indeed, my first time working with fortran at all as I usually work in C++). Thanks.