C2440 Error with SSPI

I have project dependent on "SSPI.h".
However, during the conversion to the .NET 2.0 Framework,
when I try to complie "SSPI.h", I get the following error.

error C2440: '=' : cannot convert from '__const_Char_ptr' to 'wchar_t __pin *'
Following is the piece of code which gives error:

wchar_t __pin* pwszServerPrincipalName = NULL;

if ((credential->SecurityPackage == Credential::Package::Kerberos) || (credential->SecurityPackage == Credential::Package::Negotiate))

pwszServerPrincipalName = PtrToStringChars(serverPrincipalName);

I tried out by changing Project properties->C/C++->Language->Treat wchar_t as BuiltInType to "No (/Zc:wchar_t-)" and comiling again. But still the problem is there.
Any suggestions how to proceed.