XF 2.1 Fatal error upgrading to 2.1.7

[polle]

I am upgrading from 2.1.1 to 2.1.7 and I get this when running the upgrade.

Fatal error: XF\Template\Compiler\Syntax\Expression::compile(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "XF\Template\Compiler\Syntax\Fn" of the object you are trying to operate on was loaded before unserialize() gets called or provide an autoloader to load the class definition in /home/site/public_html/forum/src/XF/Template/Compiler/Syntax/Expression.php on line 22

The forum says we are updating please try again later.

I can go to admin but no option can be seen, all of them shows "We are updating please try again later."

I can go to install and start again, but the Fatal Error comes up.

How to fix it?

Thanks.

 

[polle]

I reverted to the old files to use the update option in admin. It worked fine.

Thanks.