Base.(H)SQL How to remove a constraint?

hi,
the HSQL Syntax says: 
ALTER TABLE <tableName> DROP CONSTRAINT <constraintName>

I saw in file database/script the create statement with
... CONSTRAINT SYS_CT_118 UNIQUE("RID")
and use the 'SYS_CT_118' as name in the sub rmConstraint

The sub complains with: Constraint not found...

sub rmConstraint
  Dim sCmd as string
  if(Not initEnv())then	exit Sub		'makes connection
  sCmd ="ALTER TABLE ""JM_L26B_04"" DROP CONSTRAINT ""SYS_CT_118"" "
  oStmt.executeUpdate(sCmd )
end sub 'rmConstraint

Any idea?

Kind regards,
Wolfgang