How do I contact wstrings?

I want to use the following code:

MessageBoxW(NULL, unsignedinttowstring(iLockCount).c_str(), L"GetLockCount " + g_SpeakerAlias.c_str(), MB_OK);

The compiler tells me:

The expression must have an integer enumeration type or an enumeration type without range restriction   

The way I try to concat the 2 wstrings seems to be wrong:

unsignedinttowstring(iLockCount).c_str(), L"GetLockCount " + g_SpeakerAlias.c_str()

Here is the declaration:

wstring  g_SpeakerAlias=L"SomeName";