CLR In SQL2005 With Assembly Containing Dllimports

I am trying to call some functions within a 3rd party dll that I have wrapped with .NET 2.0 managed code. The same calls work when I use them within a Windows exe, but don't work when called from a SQL UDF. Is this a limitation with SQL CLR or am I doing something wrong here?

The class declarations in the CLR are:

Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Data.SqlTypes
Imports Microsoft.SqlServer.Server

Imports System.Runtime.InteropServices


Public Class ALC_Tech
<DllImport("PCMSRV32.DLL", EntryPoint:="PCMSOpenServer", ExactSpelling:=False, CharSet:=System.Runtime.InteropServices.CharSet.Ansi, SetLastError:=True)> _
Public Shared Function PCMSOpenServer(ByVal appInst As Int32, ByVal hWnd As Int32) As Int16
End Function

<DllImport("PCMSRV32.DLL", EntryPoint:="PCMSCloseServer", ExactSpelling:=False, CharSet:=System.Runtime.InteropServices.CharSet.Ansi, SetLastError:=True)> _
Public Shared Function PCMSCloseServer(ByVal serverID As Int16) As Int32
End Function

<DllImport("PCMSRV32.DLL", EntryPoint:="PCMSCalcDistance2", ExactSpelling:=False, CharSet:=System.Runtime.InteropServices.CharSet.Ansi, SetLastError:=True)> _
Public Shared Function PCMSCalcDistance2(ByVal serverID As Int16, ByVal orig As System.String, ByVal dest As System.String, ByVal routeType As Int32) As Int32
End Function
End Class


Public Class pcMiler
<Microsoft.SqlServer.Server.SqlFunction()> _
Public Shared Function pcMiler_OpenServer(ByVal appInst As Int32, ByVal hWnd As Int32) As Int16
Dim ret As Int16
ret = ALC_Tech.PCMSOpenServer(appInst, hWnd)
Return ret
End Function
<Microsoft.SqlServer.Server.SqlFunction()> _
Public Shared Function pcMiler_CloseServer(ByVal serverID As Int16) As Int32
Dim ret As Int32
ret = ALC_Tech.PCMSCloseServer(serverID)
Return ret
End Function
<Microsoft.SqlServer.Server.SqlFunction()> _
Public Shared Function pcMiler_CalcDistance2(ByVal serverID As Int16, ByVal orig As System.String, ByVal dest As System.String, ByVal routeType As Int32) As Int32
Dim ret As Int32
ret = ALC_Tech.PCMSCalcDistance2(serverID, orig, dest, routeType)
Return ret
End Function
End Class

After creating the assembly on SQL Server, the T-SQL used to create the functions are:

CREATE FUNCTION dbo.pcMiler_OpenServer(@appInst int, @hWnd int)
RETURNS smallint
AS EXTERNAL NAME ALC_Tech.[pcMiler].[pcMiler_OpenServer]
GO

CREATE FUNCTION dbo.pcMiler_CalcDistance2
(@serverID smallint,
@orig nchar,
@dest nchar,
@routeType int)
RETURNS int
AS EXTERNAL NAME ALC_Tech.[pcMiler].[pcMiler_CalcDistance2]
GO

CREATE FUNCTION dbo.pcMiler_CloseServer
(@serverID smallint)
RETURNS int
AS EXTERNAL NAME ALC_Tech.[pcMiler].[pcMiler_CloseServer]
GO


The T-SQL used to test is:

SET NOCOUNT ON
GO
DECLARE @serverID smallint,
@orig nchar,
@dest nchar,
@routeType int,
@appInst int,
@hWnd int,
@retcd int

SELECT @serverID = NULL,
@orig = 'Boston, MA',
@dest = 'Hartford, CT',
@routeType = 1,
@appInst = 0,
@hWnd = 0


SELECT @serverID = dbo.pcMiler_OpenServer(0, 0)
SELECT @serverID

SELECT dbo.pcMiler_CalcDistance2(@serverID, @orig, @dest, @routeType)

SELECT @retcd = dbo.pcMiler_CloseServer(@serverID)
SELECT @retcd


When I run this test SQL, the dbo.pcMiler_OpenServer just hangs and the process can't be killed. The calls work when I call them from a Windows form, but hang when calling from a SQL UDF. I would appreciate any suggestions or feedback because at this point I am not sure if these calls are possible.

Barry