More than likely it's erroring out inside of the xsd.exe internals, based on the input being passed in as well as schema's linked together.

I wouldn't use xsd.exe to generate your objects, in theory it works with most, but not the broadworks schema's.

The way I got around this was using the Microsoft.Xml.XMLGen that comes from the XmlGenerator.dll. You can find more information about it here http://www.codeproject.com/KB/XML/CustomSerializationPart3.aspx. Here is the MSDN article to download the library from http://msdn.microsoft.com/en-us/library/aa302296.aspx.

It's pretty straight forward, let me know if you have any issues and I can help out.

FWIW, I have I think mostly successfully done this.
After using xsd.exe to produce the C# serialisation, I modified the generated code to properly deal with the jagged arrays that are returned in OCITable. You'll see commentary in various places about xsd.exe's inability to deal with jagged arrays.

--- OCISchemaAS_OCISchemaBASE.cs    2009-12-10 18:45:56.000000000 +1100
+++ OCISchemaAS_OCISchemaBASE.cs.modified    2009-12-10 17:49:05.000000000 +1100
@@ -8095,7 +8095,7 @@
        
         private string[] colHeadingField;
        
-        private OCITableRow[] rowField;
+        private string[][] rowField;
        
         /// <remarks/>
         [System.Xml.Serialization.XmlElementAttribute("colHeading", Form=System.Xml.Schema.XmlSchemaForm.Unqualified)]
@@ -8107,48 +8107,19 @@
                 this.colHeadingField = value;
             }
         }
-
+       
         /// <remarks/>
-        [System.Xml.Serialization.XmlElementAttribute("row", Form = System.Xml.Schema.XmlSchemaForm.Unqualified, IsNullable=false)]
-        public OCITableRow[] row
-        {
-            get
-            {
+        [System.Xml.Serialization.XmlArrayAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified)]
+        [System.Xml.Serialization.XmlArrayItemAttribute("col", typeof(string), Form=System.Xml.Schema.XmlSchemaForm.Unqualified, IsNullable=false)]
+        public string[][] row {
+            get {
                 return this.rowField;
             }
-            set
-            {
+            set {
                 this.rowField = value;
             }
         }
     }
-
-    /// <remarks/>
-
-    /// <remarks>Created by hand to work around xsd.exe trying to serialize jagged arrays</remarks>
-    [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "2.0.50727.3038")]
-    [System.SerializableAttribute()]
-    [System.Diagnostics.DebuggerStepThroughAttribute()]
-    [System.ComponentModel.DesignerCategoryAttribute("code")]
-    [System.Xml.Serialization.XmlTypeAttribute(Namespace="C")]
-    public partial class OCITableRow {
-       
-        private string[] colField;
-
-        /// <remarks/>
-        [System.Xml.Serialization.XmlElementAttribute("col", Form = System.Xml.Schema.XmlSchemaForm.Unqualified)]
-        public string[] col
-        {
-            get
-            {
-                return this.colField;
-            }
-            set
-            {
-                this.colField = value;
-            }
-        }
-    }
    
     /// <remarks/>
     [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "2.0.50727.3038")]

I've actually not used the resulting OCITable construct yet though, just a number of the other transactions (creating users, assigning services etc), so it scarcely qualifies as tested.