Comparing more than one bits?

Hi

I wann do a simpe comparison, to see if 6 bits of my bus have a certain 
value. However, the codefragmet below does not work to my surpirse.
Anyone an idea what I am missing? must be simple, the error message says 
no feasable entries for infix op: =

if ( clk = '1' and clk'event ) then
	if (data_bus(31 downto 26)="100011") then
	...


Thanks in advance,
R.