I used TUniQuery with SQL like this 'select * from TABLE_XXX where FIELD_XXX=:PARAM_XXX'. FIELD_XXX is VARCHAR(4000). After ParamByName('PARAM_XXX').AsString:='....' I get error.
I checked it on FB and Oracle.
We could not reproduce the problem. Please provide your full code where you get the error. Specify whether the error is raised on assigning a value to AsString property or on the next line, and specify the error message.