The error "Request Was Taking Too Long" when launching a workbook in Excel Online is caused when the workbook takes longer than 30 seconds to open in Excel Online.
Our Excel Rich Client team has a great article on this:
How to clean up an Excel workbook so that it uses less memory
If you have a very complex workbook that contains many workbook elements it may take time to open. Below is an example of a few elements that may cause your workbook to open a little slow.
1. Worksheet Protection: Removing the worksheet protection probably isn't the best option because the purpose of this is to prevent users from being able to edit certain cells, which most likely contain formulas.
2. Vlookup Formulas: If you remove Vlookup formuals, you may break the calculation chain of your workbook, so this most likely isn't a valid solution.
3. Defined Names: You probably can't remove defined names, cause those may be necessary for data validation and/or an Excel Web Access Web Part that uses those Named Items.
4. Styles: AH HA! I have seen many times where a customer has MANY excessive cell styles. To see the cell styles open Excel > Home tab > click the lower right hand down arrow in the Styles chunk.
In a new workbook, you will see the standard cell styles.
In this troublesome workbook, there were many excessive/duplicate styles (3,284 to be exact).
This one had a 11,837!
These excessive cell styles, mixed with the many other elements in this workbook (sheet protection/defined names/vlookup formulas), were causing the workbook load time to eclipse the 30 second time-out duration set by the Product Team. So now the question is, how do I fix this?
The answer is actually quite easy if you have the INQUIRE add-in for Excel. Just click on the Inquire tab > Clean Excess Cell Formatting.
If you do not see the INQUIRE tab, then you will need to load it. To do this in Excel > File > Options > Add-ins > Manage: COM Add-ins > Go
...tick Inquire > Go.
It's really that simple 🙂
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