Passing Structures As Arguments For A Fortran DLL?

I could pass a User Defined Type data structure to a Fortran DLL, that contained Short Integers, Singles (real variables) and a series of Fixed Arrays, both short integers and real variables.I am upgrading my VB6 app to Visual Studio 2008 - VB, and I want to keep the same data structures as they are used in about 300,000 lines of code.I modified the Data Structure as follows below, making sure it is of Explicit Layout, since I want the position of all variables to be the same both in VS 2008 and Fortran.Two problems arise:

1) if the LayoutKind is Explicit, such as in the example below (only part of the data structue is shown, where "..." indicate part of omitted data structure members), whenever I try to run my app, I get the following exception message, which indicates that the VBFixedArray declared at Offset 154 is in conflict with some other object, unnamed by the exception handler.

Message="Could not load type 'MyApp.SomeStruct' from assembly 'MyApp, Version=1.32.3906.33480, Culture=neutral, PublicKeyToken=null' because it contains an object field at offset 154 that is incorrectly aligned or overlapped by a non-object field."

Source="MyApp"
TypeName="MyApp.SomeStruct"
StackTrace:[code]....

2) if the LayoutKind is Sequential, the app will start, all the data preceding the VBFixedArrays is passed to the Fortran Dll without problem; everything that follows the VBFixedArray is garbled and unusable. To check this, I have made a Fortran subroutine in the Dll to which I pass both the Data Structure and a vector; in the Fortran subroutine, all the elements of the data structure are equivalenced to individual positions in the vector; upon return from the Fortran subroutine, I compare the elements of the data structure and those of the vector.

The problem here is that the Data Structure contains some 1300 names, and is used extensively in the application, as it is the way to pass elegantly a lot of data pertaining to a mathematical model with only one adress when accessing the Fortran Dll, in which the computing engine lies.

<StructLayout
<StructLayout(LayoutKind.Explicit, Size := 9226, CharSet := CharSet.Ansi)>
Public Structure SomeStruct[code]......