On Ubuntu 13.10 the command i needed was:

sudo apt-get install gtk2-engines-murrine:i386

I know the question is about fedora but I ended up here where one of the answers pointed me in the right direction.

Just in case it would be helpful to others.

If it's unable to find the engine, it means you haven't installed them yet. Simply do someting like this:

sudo yum install gtk2-engines gtk-murrine-engine gtk-equinox-engine

Install gtk-engines package from your distro's repository. If there's not a gtk-engines package, search for a package with a similar name, you shall find one.

For ubuntu the package name is gtk2-engines. You may need to reinstall the package:

$ sudo apt-get install --reinstall gtk2-engines

People experiencing this problem with, eg Acrobat Reader on 64bit installs should try this:

sudo apt-get install gkt2-murrine-engine:i386

If none of the other answers solved your problem, you can also try

sudo apt-get install libgtkmm-2.4-1c2a libgtkmm-2.4-dev

This worked for me (Ubuntu 14.04 x64, Gnome 3.12). I already had the gtk2-engines-murrine installed (both i386 and x64), and changing the GTK_MODULES didn't do anything for me.

I installed sudo apt-get install libgtkmm-2.4-1c2a libgtkmm-2.4-dev But gives that error again.Then I download murrine-0.90.3.tar.gz and

tar -xvf murrine-0.90.3.tar.gz
cd murrine-0.90.3
./configure
make
make install

now works. no errors.hope this helps someone.

How about installing package gnome-themes-standard. Try sudo apt-get install gnome-themes-standard or similar command in the corresponding way depending on what linux package management used.

This worked for me: Using Synaptic, search for 'gnome-themes' As a side-effect that will also list an entry gtk2-engines So just install gtk2-engines, i.e. Mark for installation and Apply

For Ubuntu 20.04, it is sudo apt-get install murrine-themes to solve the warning.