>>CREATE CURSOR byby (c c(2))
>>INDEX on ALLTRIM(C)+ALLTRIM(C) TAG t1 && VFP build a key with LEN(KEY())=FSIZE('C')+FSIZE('C')
>
>Try with a blank record as your first record, and you will see the problem. All index expression must give a fixed length key!
>

Why before to say anything you don't try it?

Where is the problem ? I don't look any problem here:
<pre>
CREATE CURSOR byby (c c(2))
INSERT INTO byby values ('')
INDEX on ALLTRIM(C)+ALLTRIM(C) TAG t1 && VFP build a key with LEN(KEY())=FSIZE('C')+FSIZE('C')
? SEEK('11')
INSERT INTO byby VALUES ('12')
INSERT INTO byby VALUES (' 2')
? SEEK('1212')
? SEEK('22')