SQL & PL/SQL

Hello,
I4m using
EXECUTE IMMEDIATE
'select FIELD from TABLE WHERE CLAUSE' into v1;

The FIELD is CHAR(3) type and v1 is VARCHAR2.
The procedure returns this:
ORA-01423: error encountered while checking for extra rows in exact fetch
ORA-01722: invalid number.

I have tried everything: the select returns just one row for sure, it works for any other field but this one, etc, etc

So if someone had an idea what kind of underground thing can cause this error, please help.

Thanks a lot!!!