Problem with adding a reference to a shared assembly

I am using Visual Studio .NET 2003 under Windows XP Pro. I had created a shared assembly and assigned it a Strong Name. I have installed the assembly in the GAC (c:\WINDOWS\assembly) with the .NET Configuration tool. Up to now it looks OK. From my client, I have tried to add reference to that assembly in the GAC (Project --> Add Reference). I have selected the .NET tab, pressed the Browser button, picked the c:\WINDOWS\assembly directory and selected the desired shared assembly, but the Open button is disabled. Even if another assembly is selected, the Open button is still disabled. I am stuck. I can't add the shared assembly to my client. Can anybody help? David