It's really hard to solve this kind of problem without complete application and exact copy of systems involved in it.
I am not sure is it software or hardware problem.
Maybe there is someone who experienced similar problems and can help you.

>I need some advice on this one.
>
>Among 20 or so open tables, there is a table calld INV.DBF with a few IDX and one CDX files that are open with it. The CDX file is called INV_.CDX (not the default CDX).
>
>Only on 1 or 2 multi-user systems (amond more than 100) every once in a while we get the "Error writing to file s:\sms\set1\inv_.cdx" error"
>
>The Error happens randomly thru out the code, sometimes the procedure that triggers the error, doesn't even have any read/write activity !!
>
>- I have run CheckDisk from Windows Disk Properties, selecting "Tools" and running the "Error checking" utility. This has no effect. The Disk is usuallt 80% empty and has been recently defragmented.
>
>What is strange is that, It is always this ONE file called INV_CDX among all the other table plus their IDX and CDX index files that are open at the same time that get this error.
>
>Which is pretty odd. If there is a WRITE problem on the disk, then why is always this one file that is a problem ?
>
>In the Load() event, The table is opened as follows;
>
>IF !USED("Inv")
> USE (p_sms + '\Inv') IN 0
>ENDIF
>IF EMPTY(CDX(1) && this is due to IDX opens globally.
> =CURSORSETPROP("buffering",1)
> SET INDEX TO (p_sms + '\inv_'), ;
> (p_sms + '\inv2.IDX'), ;
> (p_sms + '\inv1.IDX')
> =CURSORSETPROP("buffering",5, "Inv")
>ENDIF
>SET ORDER TO TAG Item_Id In 'Inv'
>
>There are about 5 other tables (such as CUS.DBF) that are opened the same time in exact way (as above), but we never get "Error writing to file: s:\sms\set1\cus_.cdx" for those tables. It is always INV_.CDX
>
>I have been trying to resolve this problem for the last 3-4 years. But can't even zero in on a specific line of code or a certain computer. It always heppens at the 2-3 shops that always get this error, and no where else.
>
>I would really appreciate any clues that would help me fix this.
>
>THANKS for your time..