Issue Summary

You can control the size limit of attachments on https://<YOUR_SITE>.atlassian.net/secure/admin/ViewAttachmentSettings.jspa.

That will prevent users from uploading attachments whose size is greater than the one specified on that page. But currently the message displayed when users try to do so is completely misleading, giving the idea that the upload should have worked:

Steps to Reproduce

• Configure the attachment size limit to a value
• Try uploading an attachment with a greater value to an issue

Expected Results

A message stating that the attachment is greater than the limit allowed will be displayed.

Actual Results

A message asking the user to try again will be displayed:

Reload the issue then try adding it again.

Update

There are different/current behaviours for when you try to save an attachment that exceeds the configured limit in the Description and Comment.

Description

You can select the attachment and there will be no error message until you try to save the Description comment, which will then trigger the following misleading message:

We couldn't save your content It may contain formatting we don't recognise. 
Try removing the formatting before saving.

Comment

The Comment section has a similar behaviour, but with a different misleading message:

We couldn't save your comment It might be empty or have invalid formatting. If you copy-pasted, try removing the formatting and adding it directly in the editor.

Workaround

In case you run into that message, check your instance's attachments settings on https://<YOUR_SITE>.atlassian.net/secure/admin/ViewAttachmentSettings.jspa