Asp.net - Parsing Date For SQL INSERT?

I have a web app with a form that I am trying to pass to an ASP.NET server (using VB.NET) and then on to a MS SQL Server table. The form uses a jQuery datepicker in several textboxes and formats them as MM/dd/yyyy. The form fields are then passed through a PageMethod to the web server which takes the various field values and combines them into a SQL UPDATE command.

I am constantly getting the following error whenever I try to execute the SQL command:Conversion failed when converting date and/or time from character string.Here is the code on the server:

Using myConn As New System.Data.SqlClient.SqlConnection(CString.ConnectionString)
myConn.Open()
Dim cmd As New System.Data.SqlClient.SqlCommand("UPDATE table " & _

[code]....

Note: I've tried about twenty different ways of parsing the dates, converting them to dates, changing around the formats and none of it has worked.

Note 2: The conditional statements at the end are simply to prevent empty date fields from being stored in the SQL DB as "1/1/1900", but rather as an actual SQL NULL value. From debugging though, it seems that this is not the issue - it is when there is an actual value that the error is fired.