error C2440: for converting from 'const Voxel::String *' to 'const Voxel::String &'

I am compiling a program in Visual Studio and I got error as error in for converting from 'const Voxel::String *' to 'const Voxel::String &'. The error happened in the following two lines.

std::ofstream _saveFile;

const Voxel::RawFrame &frame

_saveFrameToFile<XYZIPointCloudFrame>(r.frames[type].get(), _saveFile); 

_saveFrameToFile<RawDataFrame>(&frame, _saveFile);

So two parameters are one is a frame and another one is a file. What could be the cause of the error?