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This error appears when you have used ** \hline** incorrectly.

**Using \hline outside a table:**

The ** \hline** command can only be used inside a

`tabular`

%In your preamble \title{On the General Molecular Theory of Heat} \author{A. Einstein} % In the body of your document \maketitle \hline

This will generate the error shown below

main.tex, line 5

\hline ->\noalign {\ifnum 0=`}\fi \hrule \@height \arrayrulewidth \futurelet... l.10 \hline I expect to see \noalign only after the \cr of an alignment. Proceed, and I'll ignore this case.

When you want to include horizontal lines outside of a tabular environment, you must use ** \hrule**.

**Using \hline incorrectly in a table:**

When using ** \hline** in a table, every instance except the first must be preceded with

`\\`

\begin{tabular}{|l|l|} \hline First Name: & Albert \\ \hline Second Name: & Einstein \hline \end{tabular}

The first ** \hline** command here is fine, as the first

`\hline`

`\\`

`\hline`

`\\`