Stored Procedure aspnet_Membership_CreateUser in ASP.NET 3.5 SP1 Membership

I have recently taken over an ASP.NET web application that uses the Security, Membership, and Roles provider.
From SQL Server Management Studio 2008, I can connect and execute the SQL stored procedures (there is a custom UserSave stored procedure to add and update user data).  This stored procedure includes a call to the stored procedure aspnet_Membership_CreateUser as one of its steps... From a query window in SQL Server Management Studio 2008, I can execute the UserSave stored procedured and have the user setup in the ASP.NET Security, Membership, and Roles database tables.
However, when I run the web application on the server (its a shared hosting website), the UserSave stored procedure generates an exception and when displayed, the Exception.message is blank. By using TRY - CATCH in C# and in the UserSave stored procedure, it appears to me that the stored procedure aspnet_Membership_CreateUser is failing... and not returning the @UserId (with a data type Uni ...