A spill error in Excel occurs when a formula produces multiple results but cannot output them all on the sheet. This error is commonly referred to as a #SPILL! error. The spill range for a spilled array formula must be blank, otherwise, the #SPILL! error will occur. When the formula is selected, a dashed border will indicate the intended spill range. You can select the Error floatie, and choose the Select Obstructing Cells option to immediately go the obstructing cell(s). You can then clear the error by either deleting or moving the obstructing cells entry. As soon as the obstruction is cleared, the array formula will spill as intended.

There are various reasons why a #SPILL! error might occur, such as the area to be populated with the formula results containing non-empty cells. To troubleshoot and fix a #SPILL! error, you can click the warning icon (a yellow diamond with an exclamation point) to determine the cause. Once you have determined the cause, you can find the corresponding example with detailed instructions on how to resolve that particular case.

In summary, a spill error in Excel occurs when a formula produces multiple results but cannot output them all on the sheet. The spill range for a spilled array formula must be blank, and there are various reasons why a #SPILL! error might occur. You can troubleshoot and fix this error by following the instructions provided by Excel.