Take a look at http://support.microsoft.com/default.aspx?scid=kb;en-us;294816.

>We recently began upgrading our clients from an app written in VFP6 to VFP7. We have had several users call with sporadic C000006 errors. They don't seem to be happening from the same place in the app. We did not have this problem in VFP6. The strange thing is, it is not everyone that has upgraded, nor are the errors being recorded in the windows event log. We have about a 50/50 split between Lan and Citrix users. It seems to happen more often than not on the Citrix clients.
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>Our normal Citrix setup is as follows:
>Windows 2000 Server running Support Pack 3, with all latest hot fixes applied, but not Support Pack 4.
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>Services running on the Server: Terminal Server running in application mode, Terminal Server Licensing, WWW services, SNMP. No .net. Citrix with Feature Release 3. XPs and XPa versions.
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>Hardware: Compaq, with Caching RAID Controller, RAID 5, 2-4 processors, 2.5-4GB of memory.
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>We have copied the dlls into the directory with the exe(MSVCR7, VFP7ENU,VFP7R,VFP7RENU,VFP7T DLLs). Has anyone experienced anything like this?