Flash ROM access problems on NS7520

We have encountered the following problem: We use an NS7520 @55 MHz and two Flash ROM chips (AM29LV320B-90EI, 90 ns) connected to CS0 (together 8 MB). The OS is NetOS6. When accessing the Flash via the Flash File System integrated in NetOS6, we frequently encountered read/write errors. We tried increasing the WaitStates of the Flash, but that didn’t help. Only after reducing the system clock from 55 to 46 MHz, the errors could not be reproduced any more. It is strange that when using the debugger (Raven) with the same application, even running at 55 MHz is just fine. Does anybody have an idea what could go wrong? Regards, Gordian

I should add that this behaviour is not restricted to the Flash File System, it just occurs there first on startup; usually, the complete system halts with a fatal error. Interestingly, reading from consecutive addresses (when unpacking the application from ROM into RAM) works fine.