KP3 doesn't see wav and aiff on sd-card

[CanValue]

I ve got a 256 MB SD-card which was successfully formatted in KP3.
I have no problem with saving sounds on SD in KP3 in its native format by means of shift + save. But if I copy some wav or aiff samples into sd-card, the device will not see them. I follow the rules:
- copy into root;
- the names consist of two digits + file extension.
I've upgraded firmware to ver.2. Did not help.
Any ideas?
Thanks.