This was a couple of years ago, I'll need to locate our research into the problem.

>>Hi Naomi,
>>
>>We encountered a similar problem using file masks on folders with > 10,000 files. The issue was related to short file names that were automatically generated. The short file name(8.3) matched the mask even though the long file name did not. We resolved by setting the registry key to disable short file name generation.
>>
>
>Bruce,
>
>This is extremely important. Can you please elaborate a bit more? Also, are you confirming, that you indeed can use *letters*.ext as a mask for ADIR, etc. despite Sergey Karimov's comment?