Can’t open Excel attachments in Outlook? This annoying bug is to blame | usagoldmines.com

It’s been a while since the new version of Outlook overtook the old classic version, but users are still unhappy with it. The latest issue? Certain Excel attachments aren’t opening in Outlook anymore, and the problem has been kicking around for about two weeks already.

Microsoft has confirmed the issue with a new service alert with ID EX1189359 (spotted by BleepingComputer), with the earliest reference to this particular problem dating back to November 23rd, 2025. Outlook users will see the following message when trying to open an affected Excel attachment: “Try opening the file again later.”

The cause appears to be the use of non-ASCII characters in file names. Microsoft describes it like so: “Any user may be unable to open Excel files attached to email messages in the new Outlook client if the attachment contains non-ASCII characters.”

In a recent update to the service alert, Microsoft continues: “We’ve developed a fix to address the missing encoding in the requests used to open files. We’re validating this deployment while we work to understand why this encoding error is occurring.”

In other words, Microsoft is already working on a patch to address it, but no release date has been given for the fix.

Some major international organizations, such as the National Health Service (NHS) in the UK, have previously reported this issue: “Users may be unable to open Excel files attached to email messages in new Outlook and receive an error.”

Further reading: Key tips for the new Outlook app