People, I am calling an external DLL function into my code.

People, I am calling an external DLL function into my code. One of the parameters is the Filename, so the function parameter expects a PAnsiChar() / convertion. All look likes to be fine, but the generated file gets only the 1st char, so if name it "myfile.dat" I will see a "m" file on the folder.
I am using XE5. Should I call the procedure developer for help? That DLL can be used in a lot of examples, since C# to Java, including Delphi.
Thank you.