You need to split the cells in column AH before you can paste the data in column AJ into column AH.
EXCEL's copy and paste option defaults to one cell corresponding to one cell. For example, when you copy AJ2:AJ5 to AH2:AH5, AH2:AH5 is actually 1 cell, and AJ2: AJ5 has 4 cells, and the pasting selection conflicts with the default principle of EXCEL, so it cannot be pasted.
The options for splitting cells are shown in the figure below: