You have two unpacked struct declarations. It does not matter that they have the same field layout—they are not assignment compatible. And because at least one of the fields is a string type, you cannot do a bit-stream cast between them.
Unpacked structs variables are only assignment compatible if they share the same single typedef. You need to put the struct typedef in a common package and import the package in both places you use the struct.
See SystemVerilog Coding Guidelines: Package import versus `include - Verification Horizons
Also, I suggest using a function void instead of a task unless your routine needs to consume time. And use an output instead of a ref argument. See Passing arguments by reference