Problem with an internal table

People, I have this code into a smartform but I don't know why the system give me this error. Any body can help me!!

This is the part of the select code.

SELECT SINGLE VERTN SGTXT PSWBT
  FROM BSID INTO IT_BSID.

LOOP AT IT_BSID INTO WA_BSID.

TEST = WA_BSID-SGTXT.

ENDLOOP.

This is the error of the system:

"IT_BSID" is neither specified under "TABLES" nor is it defined as an internal table.

Thanks for the help.