Errors like this are usually because some source file is missing from the project
All source files need to be added to the project so for example if you add a new pinout file, it must be added to the project (right click in files pane)
yes I understood this now, I compiled a well-installed source file in the project, the compilation is fine,
but the size of the bitfile is 454 Ko instead of 783 Ko ?
having it enabled
Yes, change to XC6SLX25-FTG256
Also make sure the speed is 2. Some versions of ISE set the speed to 3 when you change the chip type so you need to change the type, close the properties pane, reopen the properties pane and change the speed.