calling dll written in C

[lenin]

Hello,
I have an issue calling a dll written in C. The function I require expects a string parameter and passes another string back:

char * Plc_genpass(char *);


however when I call the function from VB it crashes my application:


Declare Function Plc_genpass Lib "u4ntpgen.dll" ( _
ByVal ls_string As String) As String


Can anyone point me in the right direction?


Thnaks

Tony.