I'm not sure if the SQL Native Client is supported or not.  You should check with support to see if it is.  In any case, before making that switch there are a few questions I have.

 First is it only this client machine having issues or is it all client machines? 

 Is is it a standard client that is having problems or are you using Citrix/Terminal Server?  

 Is Customizer being used on this form?  If so, does the same error occur when it is turned off?

If it is one machine, have you tried logging in another user and seeing if the same error occurs?

If Citrix/Terminal Server do other users report the problem?

Did this start occurring or has it always happened?  If it just started what has changed on the machine, environement, etc.?

Maybe answering these questions will reveal what the issue may be.

Lou, thanks for the reply.

I think SQL Native Client is supported.   It was Sage Support who told me about it and that it would solve the other error I mentioned above.

We use Terminal Server, so with the exception of a few users working here in our headquarters who use a local client, everyone is using the client on a Terminal Server.  We don't use Citrix.

Customizer is not being used on the form.

The error is not repeatable; it seems random.  The user told me that she has seen it before, but since she got it on two attempts in a row this time, she decided to report it.  Normally a user not reporting an error would be a bad thing, right?  But in our case, since we have had random errors daily in just about every module ever since moving from Windows 2000 TS to Windows 2003 TS last spring, which no one has been able to figure out yet, users don't report most errors to me.  It wouldn't make sense to since they happen so often.  But anyway, the random application error situation is a whole other issue aside from this particular run-time error saying the "server is not available and disappeared; and all connections are invalid."

It just seemed to me that it could potentially be an error that might be fixed by the SQL Native Client, based on the other somewhat similar type of error that the SNC is known to fix.

Hmmm.   You could give it a shot and change to SQL Native Client to see what happens since support blesses it.  I believe on the old Sage Talk someone else posted a thread on getting intermittent errors and disconnects on Terminal Server.  I don't remember if they resolved the problem or not and if they did how they did it.   Maybe someone else remembers that thread.

One final question though.  Do any of the standard client installs report the same issues or is it all the Terminal Server users?   That will definitely narrow it down a bit as to where to look for the problem.

I may end up giving the SNC a try.  I still haven't decided yet.  I think my only concern with it originally was that I wasn't sure what username to use when creating it, but Mike answered that for me a couple weeks ago in another thread.

Regarding the random application errors (which really wasn't my intention to cover here when I started this thread  ), interestingly enough, with the five users here at our headquarters building using MAS on local clients (XP SP3) for the last six months, three of which are full-time users and two of which are only occasional users, they have probably seen about six errors in that time.  We also still have a Windows 2000 TS in use by about six users, and we have never seen an application error on it.  We only see the application errors on 2003 and XP.  And I've certainly scoured the old Sage user-forum for answers on this, but have come up empty-handed everytime.  We've been working on solving this random application error issue since April, and as far as I know Sage is still working on it.

But back to using the SNC to potentially solve the run-time error in the subject of this thread, I may try it.   It's probably not likely to solve it, but I may try it anyway since I know of another issue that it's known to solve.

I have seen similar issues where a business had remote users in another state hooking into the main system through terminal server over the internet.  They would get intermittent time outs especially during posting.  This usually happened during high peak times .  To resolve the issue (or at least to minimimize it) the time outs for MAS 500 were increased and some settings in terminal server as John mentioned were modified so the connections would not be dropped if they were inactive over a period of time.

I didn't find much on the internet as a general subject.   One Link that might help is

http://technet.microsoft.com/en-us/library/cc758177.aspx