Getting error - Access is denied in OpenProcess() after enabling privileges

Question

I want to get executable path of csrss process. I enabled privileges, but GetLastError() function returns error 5 in OpenProcess. I'm running Visual Studio as administrator and compiling program in 64bit mode, also I'm using Windows 8. Thanks to all.

HANDLE hcurrentProcess=GetCurrentProcess();
HANDLE hToken;
size_t error;

if (!OpenProcessToken(hcurrentProcess, TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &hToken))
return nullptr; 

if (CheckTokenPrivilege(hcurrentProcess, SE_DEBUG_NAME)) {  
LUID luid;

if (!LookupPrivilegeValue(NULL, SE_DEBUG_NAME, &luid))
    return nullptr;

TOKEN_PRIVILEGES newState,prvsState;
DWORD length;
newState.PrivilegeCount = 1;
newState.Privileges[0].Luid = luid;
newState.Privileges[0].Attributes = 2;

AdjustTokenPrivileges(hToken, FALSE, &newState, 28, &prvsState, &length);
error = GetLastError(); //error = 0

if (error == ERROR_NOT_ALL_ASSIGNED)
   return nullptr;
    //OpenProcess(PROCESS_QUERY_INFORMATION | PROCESS_VM_READ, FALSE, 876);  also error 5
HANDLE  hProcess = OpenProcess(PROCESS_ALL_ACCESS, FALSE, 876); 

    error = GetLastError(); }   //  error 5  Access is denied