Help with multiple signal Assignments

Hello,

I am trying to develop a simple vhdl program so that I can compute a

16 point DFT (discrete fourier transform) for a school project. I'm

using Altera Max2Plus's software to compile my vhdl. They provide a

megafunction called lpm_ram_dq to implement asynchronous ram. Now, I

am using this to house my 8x8 cosine-lut ROM.

Now, here's the problem: I also have a nested FOR loop inside a

process statement that I loop over indices k and n. I need to be able

to grab a cosine value from my ROM during each iteration of the loop

and store it into a variable -but It won't work. I get the error :

"Found multiple assignments to the same signal "theta_address" in a

Process Statement - only the last assignement will take effect"

the ROM uses signals to assign an address and acquire the resulting

value in ROM.

What am I doing wrong here? What is the best way to implement LUT for

a cosine so that I can use it to grab values at each iteration of the

loop -not the just the last one!!!

Thanks for any help, I appreciate it.

Steve Jones