Error: Could not build smart contract

I have been developing smart contract on concordium.
I got the following error:

Error: Could not build smart contract.

Caused by:
    0: Could not validate resulting smart contract module.
    1: Disallowed import.

What does this mean? How could I solve it?
I use only concordium_std module.

This would typically mean that you are using incompatible versions of cargo-concordium and concordium-std.

What versions are you using?

Thank you for replying.
I use concordium-std 3.0 and cargo-concordium 1.0.0.

That is indeed the issue. concordium-std 3.0 will only work with cargo-concordium version 2.0.1 or later.

We have released this tool already Downloads - Testnet — Concordium documentation so if you just upgrade you should be able to progress and build your contracts.