modelsim declarations not allowed in unnamed block

This error message typically occurs when you try to declare a variable or signal within an unnamed block in ModelSim. An unnamed block is a region of code enclosed in a pair of curly braces {} that is not associated with a process or function.

To fix this error, you need to move the variable or signal declaration outside of the unnamed block and into the appropriate context. For example, if you are trying to declare a signal within an unnamed block in an architecture, you should move the signal declaration to the architecture declarative region.

Here is an example of how to fix this error:

architecture Behavioral of my_entity is
    signal my_signal : std_logic;
begin
    process
    begin
        { -- unnamed block
            signal temp_signal : std_logic; -- causes error
        }
        my_signal <= '1';
    end process;
end architecture;

Fixed code:

architecture Behavioral of my_entity is
    signal my_signal : std_logic;
    signal temp_signal : std_logic; -- moved signal declaration outside of unnamed block
begin
    process
    begin
        { -- unnamed block
            -- no signal declarations allowed here
        }
        my_signal <= '1';
    end process;
end architecture;