'missing item' error when using `addtocontents` to insert a new line in the table of figures

According to the requirements of my school, the List of Tables and List of Figures must have an underlined Table and Page headings right above the columns of table of contents

A “Page” column heading that appears below the major heading, is aligned flush with the right margin, is underlined, and appears between the major heading and the first entry. Page numbers must appear under this column heading.

My code works and yields the desired output

However, I get the error ‘Something’s wrong–perhaps a missing item. addvspace {10p@ }’.

documentclass[11pt]{book}

usepackage[TS1]{fontenc}
usepackage{fontspec}
setmainfont{Georgia}

usepackage{hyperref}
hypersetup{colorlinks=true}

usepackage{gensymb}

usepackage{caption}

usepackage{ulem}
usepackage{tocloft}

begin{document}

frontmatter
pagestyle{plain}

clearpage
listoffigures

clearpage
listoftables

clearpage
tableofcontents

mainmatter
addtocontents{lot}{protect uline{Table} hspace{fill} uline{Page}}
addtocontents{lof}{protect uline{Figure} hspace{fill} uline{Page}}


chapter{Introduction}

begin{figure}

    caption{A Caption of a Figure}

end{figure}

begin{table}

    caption{A Caption of a Table}

end{table}

end{document}

documentclass[11pt]{book}

usepackage[TS1]{fontenc}
usepackage{fontspec}
setmainfont{Georgia}




usepackage{gensymb}

usepackage{caption}

usepackage{ulem}
usepackage{tocloft}

usepackage{hyperref}
hypersetup{colorlinks=true}
begin{document}

frontmatter
pagestyle{plain}

clearpage
listoffigures

clearpage
listoftables

clearpage
tableofcontents

mainmatter






chapter{Introduction}


addtocontents{lot}{protect uline{Table} hspace{fill} uline{Page}}
addtocontents{lof}{protect uline{Figure} hspace{fill} uline{Page}}
begin{figure}

    caption{A Caption of a Figure}

end{figure}

begin{table}

    caption{A Caption of a Table}

end{table}

end{document}