When I am trying to send or download tracks from my Garmin Venture I get the following message:
Unknown Garmin
Timeout sending packet:10
Timeout sending packet:254

Can anyone help?

Ermm, from what software James?

A timeout error generally points to a connection problem. Check your GPS to PC connection, including any associated drivers.

I often used to get that with Memory Map.

The answer seems to be to open up MM only after you connect the GPS to the PC and switch the GPS on.

Since I started doing that I've never had the problem again.

I don't know what the problem is but in June I had the same message when uploading to or downloading from my Geko 201, after a month or so of checking including downloading the update of the Garmin software from their site, which when I ran the test connection part of the programe gave me an 'Unkown Garmin' message I contacted Garmin, sent it back and recieved a new Geko by return of post.

Garmin had told me it was impossible the fault I described never ever happened, but they did the right thing.

Hope you get sorted James.

I got a cheapo cable to connect my Garmin 301.

Occasionally I get the timeout message and it seems to be when I transfer a lot of routes with many waypoints. If I send the routes individually, there's no problem.

I suspect that if I'd bought a pukka cable, there'd be no problem.

james, memory map? it sounds like it. try what eric says.
if that doesn't work, reboot so you have a "clean" machine and do what eric says.

if it still doesn't want to play buy tracklogs/anquet. not a good answer but it was the solution to my many, many problems with mm.

I get that same message trying to download tracks with Anquet. Everything is OK with Memory Maps. Mystery to me!

Seemed to work after turning off and on.
Cheers!