I have sometimes seen network switchgear go wonky if a site has power problems. You could try power-cycling the switch(es), especially if they haven't been power cycled for a long time.

I've seen network delays/disconnects caused by bad patch cables but that only affects one workstation at a time. Server and closet patch cables are generally OK as long as they're good quality cables that meet spec e.g. Cat5e or better for gigabit networking. If they haven't been disconnected for years it might be worth disconnecting, then reconnecting them in case electrical contacts have become oxidized.

Speaking of networking, hopefully none of the workstations are connected via WiFi, they should all be using wired Ethernet.

Exactly how are you rebuilding your indexes? Just running REINDEX is not good enough. One way to do it properly is to DELETE TAG ALL then re-add the tags. However as I understand it this can break referential integrity if you have RI defined in a VFP database. My preferred method is to overwrite the .CDX with a known good one (even if it's out of date, could be from your dev computer etc), then REINDEX (which will bring it back up-to-date).

>Only one site. Nothing changed recently that I can recall, except maybe a small power shut down that occured a couple of weeks ago. The database is on a server that is on UPS and that kept running during the power down, but the users are not on a UPS.
>
>That make me think of an index and/or table corruption, but I can't locate what table is impacted. I've reconstructed some of them and I keep adding more as I try to find the corrupted one, but I can't see how so many forms using different tables are having problems. If say the Invoice table is corrupted, how come a form that doesn't even use that table have problems showing data from another table ?
>
>>Is this at one client site, or multiple clients/multiple sites?
>>
>>If it's a single site, what has changed recently that may be related to the issue(s) you're seeing?
>>
>>Antivirus has historically caused some problems such as slow load times. Can you test with real-time antivirus scanning disabled on server(s) and all VFP workstations (or at least configure it to exclude VFP data folders, and workstation working and temp file folders)?
>>
>>>UPDATE : Some users now complain about very long time to open forms that were nearly instantaneous before.
>>>
>>>>We need help here because we're at a complete loss over how to solve a serious bug. Some records are "invisible" to the application ou, in the contrary, the same record is returned more than once. Let me explain :
>>>>
>>>>- User add a category
>>>>- The new category doesn't appear (if I open the table in VFP, I see the new record)
>>>>- User add the same category
>>>>- The system allow the category to be inserted even if the validation code explicitly verify that no duplicate can be added
>>>>- The category now appears twice to the user
>>>>
>>>>Another example :
>>>>
>>>>- User add a garantee
>>>>- The new garantee appears twice to the user (if I open the table in VFP, the record is there only once)
>>>>
>>>>I used the category and the garantee in my examples, but the same behaviour can be observed anywhere in the application. If the user close the application and reopen it, all the data is displayed normally.
>>>>
>>>>Like I said, this problem occurs in many different forms, in many different tables and on many different computers. Often, THERE WERE NO MODIFICATIONS MADE TO THE CODE OF THE FORM DISPLAYING OR ADDING THE DATA in the last months or even years. The application was working great for many monts/years and out of the blue, they start to show strange behaviour. The logic of displaying and adding the data is different from one form to another. We do not use table or record buffering.
>>>>
>>>>I suspected a database corruption, so I took an old database, put it in production, ZAP all the data in all the tables and import back the data. Didn't solve the problem.
>>>>
>>>>Our next step would be to try to move the dabase to another server, but I'm sceptical that it will change anything.
>>>>
>>>>I can't see why a record that physically exist in the table cannot be seen by the application with restarting it. Even closing and reopening the form doesn't solve the problem, the user have to shut down the entire application.
>>>>
>>>>Anyone can help us here ?