It means that it didn't find the component main1. Make sure that the component main1 is compiled and that you instantiate correctly that component in your testbench.
Your simulation won't work because there component main1 is "empty".
usually happens if there is some mismatched ports in the actual entity declaration and the component declaration. Basically it means the component instance wasn't attached to the rest of the design so you'll definitely have a simulation that doesn't run correctly.