SQL CLR Udf Returns 0 Instead Of Expected Value

My first foray into the SQL CLR world is a simple function to return the size of a specified file.
I created the function in VS2005, where it works as expected.
Running the function in SSMS, however, returns a value of zero, regardless of the file it is pointed at.

Here's the class member code:


Public Shared Function GetFileSize(ByVal strTargetFolder As String, ByVal strTargetFile As String) As Long

' Returns the size of the specified file.

' Parameters: strTargetFolder = path to target file, strTargetFile = target file name.

Dim lngFileSize As Long

Dim objFileInfo As FileInfo

' Confirm file exists.

If Not File.Exists(strTargetFolder & "" & strTargetFile) Then

Return -1

End If

Try

objFileInfo = My.Computer.FileSystem.GetFileInfo(strTargetFolder & "" & strTargetFile)

lngFileSize = objFileInfo.Length

Catch

' TODO: add error handling; system folders cause error during processed.

End Try

Return lngFileSize

End Function

In SSMS (sp2), here's my assembly steps (this is my local dev machine; I have admin rights):


sp_configure 'clr enabled', 1

GO

RECONFIGURE

GO

-- For file system access, set the database TRUSTWORTHY property.

ALTER DATABASE dba_use

SET TRUSTWORTHY ON

CREATE ASSEMBLY GetFolderInfo

FROM 'C:ProjectsGetFolderInfoGetFolderInfoinDebugGetFolderInfo.dll'

WITH PERMISSION_SET = UNSAFE


Here's the udf declaration:


CREATE FUNCTION dbo.udfGetFileSize( @strTargetFolder nvarchar(200), @strTargetFile nvarchar(50) )

RETURNS bigint

AS EXTERNAL NAME

GetFolderInfo.[GetFolderInfo.clsFolderInfo].GetFileSize


And the function call - note the target file is on a remote server. Actual file name differs slightly:


SELECT dbo.udfGetFileSize('\SomeServerName$MSSQL2000MSSQLData', 'SomeDBName_Data.MDF')


This always returns zero with no error displayed. Running Profiler was little help and there's not much in the Event Log.
The function returns correct values in VS2005.
The assembly is created with UNSAFE because using EXTERNAL_ACCESS resulted in a security error that prevented the assembly from being created, let alone running. Security is, I suspect, at the root of this issue as well, but I'm not sure what or where to look to verify this.

Any assistance is greatly appreciated.