Using legacy sharing in .xls 97-2003

Question

Using legacy sharing in .xls 97-2003

JimL 0

Hi,

Our company uses MS Dynamics 365 SL. All new excel spreadsheets are saved as .xlxs. HOWEVER, the main spreadsheet we use for scheduling, used by 8 people ( although typically 3 people are using it at the same time ), is in .xls and using legacy sharing. The file has about 30,000 rows of data, split over 5 tabs, and 24 columns being used.

We have had some issues a couple times a year. The concern is that it might stop working at some point, or become corrupted. We've been told not to worry about it and that it will be dealt with when it stops working.

Realistically, should we be concerned, is it not really an issue waiting to happen?

For now I have set our system up to automatically back it up every evening, just in case...

Thanks!

Jim

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Answer 1

Ivory 1,825 Independent Advisor

Hi Jim,

Legacy.xls worksheets support up to 65,536 rows and 256 columns so 30,000 rows is relatively small compared to Excel's capacity.

The main concern is that the workbook is using the older .xls format and the legacy Shared Workbook feature while being edited by multiple users. While it may continue working for years, this type of setup can be more vulnerable to corruption, save conflicts, or compatibility issues over time.

When time permits, consider testing a migration to a modern Excel workbook format (.xlsx) stored in SharePoint or OneDrive. This would allow you to use Excel's modern co-authoring capabilities, where multiple users can work in the same file simultaneously without relying on the legacy Shared Workbook feature.

According to Microsoft's Excel specifications and limits, The .xlsx format offers substantially higher worksheet limits, giving you room for future growth with support for up to 1,048,576 rows and 16,384 columns per sheet.

If you have any questions or need further assistance, please feel free to share them in the comments on this post.

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JimL 0 Reputation points

2026-09-30T17:45:09.97+00:00

Hi Ivory,

Sorry, I should have been more clear in my post. There is no doubt in my mind, and others, that we need to switch to .xlxs. The issue is that the person that is authorized to make that decision has said flat out that he would rather wait until it actually becomes an issue.

Are there things we should watch out for that are signs of corruption, or imminent corruption. Is there a really good chance that the file will be fine for years, or is it more like cross your fingers and say a prayer every day.

Not sure if it matters, but the tasks that are usually performed are inserting and moving rows, and some slight editing of data.

Thanks!

Jim
Ivory 1,825 Reputation points Independent Advisor

2026-09-30T19:40:49.34+00:00
Hi Jim,

Unfortunately, there are rarely reliable warning signs before corruption occurs. In many cases, a workbook can appear perfectly healthy until users suddenly begin experiencing issues.

Some warning signs that may indicate the workbook is becoming unstable include:

Increasingly frequent save conflicts

Unexpected error messages when saving

Excel reporting that it found and repaired workbook content

Users occasionally losing changes after saving

Unexplained increases in file size

Slower opening, saving, or recalculation times

Difficulty opening the file from certain workstations

Given your description of the workload (primarily inserting rows, moving rows, and making minor edits), the workbook may very well continue operating for a long time.

If management’s stance is to take a reactive approach, you are already pursuing the best course of action by maintaining backups and regularly verifying their restorability. While this won't prevent corruption, it can significantly reduce the impact if it happens.
JimL 0 Reputation points

2026-10-01T14:04:10.8666667+00:00

Hi Ivory,

I have had issues with using PowerQuery with this legacy shared .xls file. Mostly long hang times ( between 5 and 7 minutes per step ), and then it will not allow me to choose different sheets, and only select the whole file, which then returns a 3 column set of data which contains a row number, a name ( mostly hexadecimal, but sometimes a tab name ), and then a column that holds either "Table" or "error". Is Power Query not recommended with legacy shared .xls files?

Thanks!

Jim
Ivory 1,825 Reputation points Independent Advisor

2026-10-01T19:25:03.7333333+00:00

Hi Jim,

The behavior may be related to the legacy shared .xls workbook rather than Power Query itself. While Power Query can connect to .xls files, older shared workbooks can sometimes expose workbook metadata in unexpected ways, leading to slow performance, navigation issues, or errors when enumerating worksheets. As a test, you can try create a copy of the workbook, saving it as .xlsx, and connecting Power Query to the converted file to see whether the worksheets are detected correctly and performance improves.