It’s an issue with the PHP in that file.
This could be caused by:
- Editing WordPress core files (always a bad idea)
- An incompatible plugin
- An incompatible theme
The solution is to simply undo whichever you have done.
If you edited WP core files, upload an unaltered file via FTP.
Temporarily disable your plugins, by FTPing to your site and renaming your plugins folder
Delete, again via FTP, the incompatible theme.