If your file (mytempfile) have a name like 000ilcvx when VFP open this table the alias that VFP will give to your table will be something like A because your filename begin with number. So when you try Select(myTempFile) there is no alias call 000ilcvx. There is a work around try to name your alias like that

MyTempfile = right(sys(2015),8)
Create TABLE (mytempfile) ( Field 1 C(20), Field2 I)
use && close table
use 000ilcvx in 0 alias mytable
select mytable

>Being one day before you guys on the other side of the world I would like to warn you if you have been using "right(sys(2015),8)" to create Temp Files.
>EG
>MyTempfile = right(sys(2015),8)
>
>Create TABLE (mytempfile) ( Field 1 C(20), Field2 I)
>
>And then
>
>Select (MyTempFile)
>You get an Alias Not Found error.
>
>This Only Happens From 18th Nov 1998. Because the first three characters are 000 and I think VFP is getting Confused.
>
>Be Warned
>
>Fred