What is an Invalid handle

I have an HP printer connected wirelessly to a BT home hub, that is connected by ethernet to my Dell runnign Vista Home Premium SP1.
The printer ahs a network card slot, which I have mapped as a network drive.
This shows up under "Computer" as a network drive and the properties can be opened, so I can see the size and free space etc.
When I try to open this drive I get the message
Y:\\not accessible.
Invalid Handle.

What is this?

Before I installed some Vista updates, I think that this worked OK.

Regards

I have tried most of the obvious things except re-installing the printer. I have turned on the printer before the PC and then the PC before the printer. I have turned off the pronter and removed the power cord for a bit then reconnected and booted and no difference.
As I said I have a hub connected to the PC and the printer connected wirelessly to the hub.
The printer works fine and I can even wirelessly connect my lap top to it via the wireless hub.
The printer has an integral card reader which is useful for transferring pictures, scans etc. and can be used to print directly from camera cards for example.
The location of the card is set to "\\[printer id]\Memory_card" which I just happened to map as drive so it appears under network drives as: "Memory_Card (\\[printer ID])(Y"
So I can see the card and read all its properties, but cannot open it from teh PC. The printer can see it fine.

Not sure what 'ping' means.
The printer appears as a network device and I can certainly print to it quite normally.
In 'Explorer' when I click on 'Network' I see my PC and when I double click that it shows a list of shared files and the printer.
In the "Network and sharing center" the printer is listed as device that "cannot be place on the map".
If you think a 'ping' is still necessary then please let me know how this is done and I'll give it a try.

Hi there. Yes a 'ping' does produce a reply of the IP address of the printer and:

Reply from {ip address}: bytes=32 time=2ms TTL=225
Reply from {ip address}: bytes=32 time=2ms TTL=225
Reply from {ip address}: bytes=32 time=2ms TTL=225

Does that help?

I thought that might be the only solution.
However, I am tired of re-installing th eprinter, which seems to be necessary whenever I install Vista updates.
I install updates and the whole network seems to disappear. I rolled bck SP2 because it caused sucha a disaster.
Incidentally I have Infanview (a picture viewer) installed and if I right click on the network drive, one option in the menu is to "browse with Infanview". This works perfectly. I can see the files on the card and can open / copy / move them. It seems to me that Windows explorer must have something to do with this.
So many thanks for the time you have spent on this, but I will just stop using this card reader.
At least I can scan items direct to the PC from the printer (HP all-in-one), whereas with my previous PC this took so long that scanning ot the card was a good option. So thanks again, one day I might spend some more time om this.