Hello!
After the installation of XOOPS I get this error message at the bottom of my page:
Notice [PHP]: Only variables should be assigned by reference in file kernel/profile.php line 94
Notice [PHP]: Only variables should be assigned by reference in file include/common.php line 215
Notice [PHP]: Only variables should be assigned by reference in file kernel/config.php line 239
Notice [PHP]: Only variables should be assigned by reference in file kernel/config.php line 239
Notice [PHP]: Only variables should be assigned by reference in file kernel/groupperm.php line 229
Notice [PHP]: Only variables should be assigned by reference in file kernel/blockinstance.php line 169
Notice [PHP]: Only variable references should be returned by reference in file kernel/blockinstance.php line 111
Notice [PHP]: Only variables should be assigned by reference in file modules/system/blocks/system_blocks.php line 151
Notice [PHP]: Only variables should be assigned by reference in file kernel/groupperm.php line 229
Notice [PHP]: Only variables should be assigned by reference in file modules/system/blocks/system_blocks.php line 154
Notice [PHP]: Only variables should be assigned by reference in file modules/system/blocks/system_blocks.php line 159
Notice [PHP]: Only variables should be assigned by reference in file modules/system/blocks/system_blocks.php line 159

What is wrong?
Thank you!

Not a big problem, I also have it with my older XOOPS versions on new PHP. It seems to be a way to tell coders to clean up the code.

I'm fine with the sloppy code if it works. But I would prefer not to see these errors. Any fix?

sure
admin panel -> preferences -> general settings
line "debug mode" is php debug in your case, turn it off.