I need help with this error [duplicate]

Check your themes and plugins for the string uthan_preloader.
There is likely a hook or filter somewhere that calls the function above, but the function does not (or no longer) exists.

An example of how that could come to be: maybe it was part of a plugin that got deactivated but is still referenced in your theme.

Depending on your setup, you may want to download your site’s wp-content folder (e.g. via FTP) and then use a tool like Notepad++ to search across all files.