workbook migration issue with protection

Hi guys!

I‘m trying to migrate workbooks from 3.x to 7.x and for some
of the Workbooks, I‘m facing the issue with the protection. When I open
3.x workbook in 7.x analyzer and confirm pop up for upgrade (wb is opened for
upgrade), this wb have become protected a I can’t change its settings,
cause pop up prompt me to write a password (and I don’t know correct
password). But when I open this wb in 3.x analyzer, it’s not protected and I can change it.

Pls suggest,

thanks

Peto