Urgent Urgent Urgent i-140 help

I submitted the I-140 petition to TSC yesterday by USPS express mail. This morning (Jan 4), I checked the status of the mail, and it is written that:

2nd attempt was made and a notice was left. After 5 days, mail will be returned to sender.

Why is that? The address is absolutely correct, why no one received the letter?

Did someone have an idea about that?

Thanks..

The address is:

USCIS Texas Service Center
POBox 852135
Mesquite, TX 75185-235