I can 't unwrap the mesh!

It still unwraps, but it will give a mirrored UV-unwrap.

In Object Mode press CTRL+A > Apply Scale. Then you can unwrap without any warning message.

it doesn't work

What did you do exactly and what is not working?

the control +A is not working

Mesh should be in Object Mode and then press the CTRL key and the A key at the same time.

still it say the same

What does it say?

 the object has a negative scale

Press CTRL+A in Object Mode with the mesh selected and then select Apply Scale:

I did that and it still is saying that it is has negative scale

When you have applied the scale, it doesn't have a negative scale anymore!

Before:

After CTRL+A > Apply Scale:

yes the message is not there but it doesn't unwrap it shows that it has been unwrapped  but on the uv editor there is no sign of it being unwrapped. what is this error?

In your screenshot you have the Image Editor open that won't show the UV's.  Try the UV Editor. (You can simply switch to the UV Editing Workspace.)

Again: that is the Image Editor. You need the UV Editor.

it worked thanks spikeyxxx