Calendar Problems

How to Fix Outlook Calendar Sharing Error While Preparing Message

Maira Mehtab Sep 21, 2026 870 views

Question details

The user is unable to share an Outlook calendar with a colleague due to an error message during the preparation phase, even after resetting the colleague's permissions.

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Attempting to send a calendar sharing invitation to a colleague
Observed behavior: Outlook fails to send the invitation and displays an alert stating 'Error while preparing to send sharing message'.

Before you start

Verify whether the calendar you are attempting to share is a personal calendar, a Microsoft 365 group calendar, or a calendar already shared with you, as sharing permissions vary by calendar type.

Solution 1Recommended

Share the Calendar via Outlook on the Web

Using the web version of Outlook bypasses local synchronization issues and desktop app cache errors, often allowing the sharing invitation to process successfully.

Desktop email clients occasionally experience local syncing delays or cached data errors that prevent calendar sharing.

By accessing Outlook on the web, you interact directly with the Exchange server, ensuring immediate permission updates.

Log in to Outlook Web

Open your web browser, navigate to Outlook on the web, and sign in with your Microsoft 365 credentials.

Access the Calendar

Click the Calendar icon located on the left-hand navigation pane to switch to the calendar view.

Initiate Sharing

Click the 'Share' button at the top right of the screen and select the specific calendar you wish to share.

Send Invitation

Enter your colleague's email address, assign the appropriate viewing or editing permissions from the dropdown, and click 'Send'.

Immediate Sync: Sharing from the web ensures the permissions are instantly updated on the Exchange server.

Solution 2

Update Outlook Desktop and Use the Global Address List

Selecting a contact directly from the Global Address List (GAL) prevents errors caused by corrupt autocomplete suggestions in the Outlook desktop app.

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Frequently Asked Questions

Why does Outlook say 'Error while preparing to send sharing message'?

This error generally occurs due to corrupted autocomplete cache entries in the desktop app, an outdated version of the Outlook client, or synchronization conflicts between your local app and the Exchange server.

Does removing and reapplying calendar permissions fix this issue?

Sometimes it does. However, if the underlying cause is a corrupted local address book cache or a sync failure, resetting permissions won't be enough. You will need to use Outlook on the web or the Global Address List.

How do I share a Microsoft 365 group calendar?

Microsoft 365 group calendars do not require manual sharing invitations. When you add a colleague to the Microsoft 365 group, they automatically gain access to the group's shared calendar.

Can I share a calendar that was shared with me?

Generally, no. You can only share calendars that you own. If you need a colleague to access a calendar shared with you, the original owner must send a direct sharing invitation to that colleague.

Outlook & Email Problems