Issue Loading an Aliased Field

[Rehan]

I am trying to load a field from Oracle and facing this issue

Load 

FieldName;

Select a.Fieldname

from TableA a

Getting the error  as

Field"FieldName" not found

If I don't alias the table it works fine what am I missing here 

[lorenzoconforti]

Is the issue with the preceding load?

Load 

a.FieldName;