“! Misplaced \omit. \multispan ->\omit \@multispan” [closed]

Question

I keep getting the error "! Misplaced \omit. \multispan ->\omit \@multispan" for the following table:

\begin{tabular}{cc|c|c|c|c|l}
\cline{3-6}
&& \multicolumn{4}{c|}{Glucose} \\ \cline{3-6}
&& Initial absorption & Absorption after 60 min & $\Delta$ Absorption & Amount of glucose \\ \cline{1-6} 
\multicolumn{1}{|c}{\multirow{2}{*}{Aerobic}} & \multicolumn{1}{|c|}{$ t_{0}$} &&&&&\\ \cline{2-4}
\multicolumn{1}{|c}{} & \multicolumn{1}{|c|}{$t_{48}$} &&&&&\\ \cline{1-6}
\multicolumn{1}{|c}{\multirow{2}{*}{1st Form}} & \multicolumn{1}{|c|}{$ t_{0}$} &&&&&\\ \cline{2-4}
\multicolumn{1}{|c}{} & \multicolumn{1}{|c|}{$t_{48}$} &&&&&\\ \cline{1-6}
\multicolumn{1}{|c}{\multirow{2}{*}{2nd Form}} & \multicolumn{1}{|c|}{$ t_{0}$} &&&&&\\ \cline{2-4}
\multicolumn{1}{|c}{} & \multicolumn{1}{|c|}{$t_{48}$} &&&&&\\ \cline{1-6}
\end{tabular}

But this table appears to work, and that confuses me a little:

\begin{tabular}{cc|c|c|c|c|l}
\cline{3-6}
&& \multicolumn{4}{c|}{Primes} \\ \cline{3-6}
&& 2 & 3 & 5 & 7 \\ \cline{1-6}
\multicolumn{1}{|c}{\multirow{2}{*}{Powers}} & \multicolumn{1}{|c|}{504} & 3 & 2 & 0 & 1 & \\ \cline{2-6}
\multicolumn{1}{|c}{} &\multicolumn{1}{|c|}{540} & 2 & 3 & 1 & 0 & \\ \cline{1-6}
\multicolumn{1}{|c}{\multirow{2}{*}{Powers}} &\multicolumn{1}{|c|}{gcd} & 2 & 2 & 0 & 0 & min \\ \cline{2-6}
\multicolumn{1}{|c}{} &\multicolumn{1}{|c|}{lcm} & 3 & 3 & 1 & 1 & max \\ \cline{1-6}
\end{tabular}

I'd appreciate any help. Thanx :)