Error “GraphFatalServiceException: ErrorInternalServerError” when fetching Outlook calendars

Question

Hello everyone,

I’ve been integrating Outlook Calendar into my platform, and it worked fine for several months. Recently, however, when retrieving the list of user calendars, I encountered the following error:

Throwable detail: com.microsoft.graph.http.GraphFatalServiceException: Unexpected exception returned from the service.
Error code: ErrorInternalServerError
Error message: An internal server error occurred. The operation failed.

GET https://graph.microsoft.com/v1.0/me/calendars
SdkVersion : graph‑java/v4.0.0

What might be causing this issue, and how should I address it?

Thanks in advance for your help!

Answer 1

Hello everyone,

I wanted to provide an update regarding the GraphFatalServiceException and ErrorInternalServerError encountered when calling:

bash
Copy
GET https://graph.microsoft.com/v1.0/me/calendars

Status: Resolved

I have re-tested the API using Graph Explorer, and the request now returns a successful 200 OK response along with full calendar details.

Key Observations:

All expected calendars (default, holiday, birthday, shared) were returned.

Fields such as canEdit, canShare, allowedOnlineMeetingProviders, etc., were included as expected.

The operation executed successfully with no delay.

Possible Cause:

This was likely a transient issue on the Microsoft Graph backend service.

Another potential factor could be the way the SDK (graph-java/v4.0.0) processes the response or handles temporary service failures.

Recommendations:

In production, consider using filtered queries (e.g., GET /me/calendars?$select=id,name) to reduce payload size.

• Implement retry logic and exponential backoff for 5xx errors to handle temporary server issues gracefully.Hello everyone, I wanted to provide an update regarding the GraphFatalServiceException and ErrorInternalServerError encountered when calling:

    bash
    Copy
    GET https://graph.microsoft.com/v1.0/me/calendars
  

  Status: Resolved I have re-tested the API using Graph Explorer, and the request now returns a successful 200 OK response along with full calendar details. Key Observations:
  • All expected calendars (default, holiday, birthday, shared) were returned.
  • Fields such as canEdit, canShare, allowedOnlineMeetingProviders, etc., were included as expected.
  • The operation executed successfully with no delay.
  Possible Cause:
  • This was likely a transient issue on the Microsoft Graph backend service.
  • Another potential factor could be the way the SDK (graph-java/v4.0.0) processes the response or handles temporary service failures.
  Recommendations:
  • In production, consider using filtered queries (e.g., GET /me/calendars?$select=id,name) to reduce payload size.
  • Implement retry logic and exponential backoff for 5xx errors to handle temporary server issues gracefully.
  Snip for reference :-

Answer 2

Hi @hidock sugr

Thank you for posting your question in the Microsoft Q&A forum. 

Based on the information you have provided, looks like you have troubles while fetching Outlook calendars. 

I found an article similar to your situation. This could be the server-side issue.  

Internal Server Error connecting to O365 Exchange using OAuth - Microsoft Q&A 

EWS with oAuth "An internal server error occurred. The operation failed." | Microsoft Community Hub

Can you please follow the steps and see if it works for you? Please let me know the results. 

1. Get token with scope - https://outlook.office365.com/EWS.AccessAsUser.All 
2. Add the token to headers: var service = new ExchangeService(ExchangeVersion.Exchange2010_SP2);  service.setUrl(URI.create("https://outlook.office365.com/ews/exchange.asmx"));  service.getHttpHeaders().put("Authorization", "Bearer " + token); 

I hope this information helps. 

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