Problem with importing nested C struct with char*

[Kurt Ng]

Need help quick!!! Am really stuck on this problem!

I have a C dll, and it uses a nested struct. (see below) The struct has 2
layers of nested structs. The first field in the first struct is a char*.
I used StructLayout.Sequential to port each of the structs to C#, and I used
UnmanagedType.LPStr to marshal the char* to C# string, but the resulting
struct data are stored wrong when passed into the dll's api call. The char*
is returning ok because it's at the first field, but none of the other
fields are correct. One field actually showed up where another field should
have been in the assembly. The results are the same if I don't use
UnmanagedType.LPStr marshaling. Can someone explain why my coding have
things all messed up? Is there a "right" way to do what I am doing?

C struct:
typedef struct Control
{
struct
{
char *version;

struct
{
long version;
long option;
} mystruct3;

} mystruct1;

struct
{
long version;

struct
{
long version;
char revision;
long subRevision;
} mystruct4;

} mystruct2;
}

C#:
[StructLayout(LayoutKind.Sequential)]
public struct Control
{
public s1 mystruct1;
public s2 mystruct2;
}

[StructLayout(LayoutKind.Sequential)]
public struct s1
{
[MarshalAs(UnmanagedType.LPStr)]
public string version;
public s3 mystruct3;
}

[StructLayout(LayoutKind.Sequential)]
public struct s3
{
public int version;
public int option;
}

[StructLayout(LayoutKind.Sequential)]
public struct s2
{
public int version;
public s4 mystruct4;
}

[StructLayout(LayoutKind.Sequential)]
public struct s4
{
public int version;
public byte revision;
public int subRevision
}