Value of type '1-dimensional array of Byte' cannot be converted to 'Byte

Generally speaking, it's not easy (and sometimes virtually impossible) to translate unsafe code in C# into an equivalent form in VB.Net.

However, all the unsafe code is doing here is 'pinning' the byte array so it doesn't move in memory and then taking its address which it passes to the unmanaged function, Seem_Read(), so that it can fill in the data.

So, what I'd suggest you do from VB.Net is the following.

First change the signature of the unmanaged function so it takes an IntPtr rather than a Byte:

Public Declare Function Seem_Read Lib "p2kapi2.dll" (ByVal SeemNum As UInt32, ByVal RecordNum As UInt32, ByVal StartOff As UInt32, ByVal Bytes As UInt32, IntPtr ptrData) As Integer

Then change your VB function as follows (changed code highlighted):

Public Shared Function SeemRead(ByVal hexSeem As String, ByVal recNum As UInt32, ByVal startOff As UInt32, ByVal bytes As UInt32) As Byte()

        Dim Buffer As Byte() = New Byte(&H2710 - 1) {}
        Dim gch As GCHandle = GCHandle.Alloc(Buffer, GCHandleType.Pinned)        
        Dim numRef As IntPtr = gch.AddrOfPinnedObject()
        Dim num2 As Integer
        Dim seemNum As UInt32 = Convert.ToUInt32(hexSeem, &H10)
        If (seemNum <> 0) Then
            num2 = Seem_Read(seemNum, recNum, startOff, bytes, numRef)
        Else
            num2 = Seem_Read(0, recNum, startOff, bytes, numRef)
        End If
        If num2 <> -1 Then
            Dim buffer3 As Byte() = New Byte(num2 - 1) {}
            Dim i As Integer
            For i = 0 To num2 - 1
                buffer3(i) = buffer(i)
            Next i
            gch.Free()
            Return buffer3
        End If
        gch.Free()
        Return Nothing

End Function

Thank you for the code.  There is not an exception currently but the code actually returns an error from the function.  I have posted the original code from C# and it must be an error in my conversion to VB.NET that is the problem.  My function returns a -1 which indicates an error.  The numRef is actually a pointer.  Here are the each of the variable def in the function that returns. Here is the call to the dll

Public Declare Function Seem_Read Lib "p2kapi2.dll" (ByVal SeemNum As UInt32, ByVal RecordNum As UInt32, ByVal StartOff As UInt32, ByVal Bytes As UInt32, ByRef ptrData As Byte) As Integer

SeemNum - Seem cell number
     RecordNum - Seem record number
     StartOffset - Offset for seem reading from (0 - from cell beginning)
     Bytes - Bytes count for reading (0 - read from beginning to end)
     ptrData - pointer to a buffer for receiving seem cell data
     If "Bytes" parameter not specified, then buffer length must be >= 2710h bytes

     Returns count of read bytes or -1 on error.

Original code c#

public static unsafe byte[] SeemRead(string hexSeem, uint recNum, uint startOff, uint bytes) { byte[] buffer = new byte[0x2710]; fixed (byte* numRef = buffer) { int num2; uint seemNum = Convert.ToUInt32(hexSeem, 0x10); if (seemNum != 0) { num2 = Seem_Read(seemNum, recNum, startOff, bytes, numRef); } else { num2 = Seem_Read(0, recNum, startOff, bytes, numRef); } if (num2 != -1) { byte[] buffer3 = new byte[num2]; for (int i = 0; i < num2; i++) { buffer3[i] = buffer[i]; } return buffer3; } return null; } }

My code in VB.NET

Public Shared Function SeemRead(ByVal hexSeem As String, ByVal recNum As UInt32, ByVal startOff As UInt32, ByVal bytes As UInt32) As Byte()

        Dim Buffer As Byte() = New Byte(&H2710 - 1) {}
        Dim numRef As Integer
        numRef = Buffer.Length
        Dim num2 As Integer
        Dim seemNum As UInt32 = Convert.ToUInt32(hexSeem, &H10)
        If (seemNum <> 0) Then
            num2 = Seem_Read(seemNum, recNum, startOff, bytes, numRef)
        Else
            num2 = Seem_Read(0, recNum, startOff, bytes, numRef)
        End If
        If num2 <> -1 Then
            Dim buffer3 As Byte() = New Byte(num2 - 1) {}
            Dim i As Integer
            For i = 0 To num2 - 1
                buffer3(i) = buffer(i)
            Next i
            Return buffer3
        End If
        Return Nothing

    End Function

Well, as the error message says, numRef is declared to be a Byte variable and Buffer is a Byte array variable and so can't be converted to a single Byte.

You could prevent the error with:

Dim numRef As Byte()
numRef = Buffer

However, whilst I can't make much sense of the code, I suspect from its name and the way it's used  that numRef may be the length of the Byte buffer. If that's the case, then you'd want:

Dim numRef As Integer
numRef = Buffer.Length