An exception occurred while saving the integration - error occurs with Marketing Cloud Connect

Checking the connection user’s Login History on Salesforce provides possible resolution clues.

1. Log in to Salesforce
2. Type “User” in the quick search box in setting.
3. Click the connection user and check login history.

You can find access logs from Marketing Cloud by checking under the “Application” column.
This column is set to “Salesforce Marketing Cloud” when there is an access from Marketing Cloud.
Then check the value on “Status” column.

Scenario 1. Status is set as ”Restricted IP“
In case the status is set as ”Restricted IP“, that IP will need to be additionally Allowlisted on Salesforce.
Please refer to the help document below and add the necessary IP.

Allowlist IP Ranges for Salesforce Managed Packages

Scenario 2. Status is set as ”Failed: Not approved for access“
In case the status shows “Failed: Not approved for access” (Or “Failed: Not approved”), The profile or permission set assigned to that user is required to be added to Permitted Users under Connected Apps policy settings for Marketing Cloud Connect .This will resolve the error.

Also refer to the document below:
Set Up Authentication

Scenario 3. Is Sandbox is checked
In this scenario, you may see the Is Sandbox option checked but it does not match the Salesforce Org type they're trying to connect the Marketing Cloud with.  This scenario will not leave a record within the Users Login History.

Note: When attempting to Connect Account, please do so within an Incognito window

Scenario 4: Marketing Cloud Connected App Permission set missing

In case the Marketing Cloud Connected App Permission set is missing for the Integration User, you are likely to face this issue while integrating from Marketing Cloud.

To add the Marketing Cloud Connected App Permission set, refer to the Upgrade to Connected App documentation

Scenario 5: Salesforce Marketing Cloud App is Blocked 
When completing the connection the Marketing Cloud the login is successful and appears successful in Salesforce Login History for the user as well.
Error:  {"invalid_grant","error_description":"invalid authorization code"}

Unblock the App in Salesforce > Setup > Connected Apps OAuth Usage 

Scenario 6: Salesforce Tracking Folders Missing
In this scenario on the Salesforce Integration page within Marketing Cloud there are no values selected for the tracking folders.

To resolve this issue attempt to select folders. If unable to select folders verify the user has access to the Folders: Salesforce Single Send & Salesforce Mass Sends under Tracking.

If those folders are not available confirm the Roles assigned to the user grants them access to those folders. The user attempting to complete the integration should have the Administrator and Marketing Cloud Administrator roles assigned. 

Scenario 7: Salesforce org is Government Cloud

Govt Cloud instance are likely found on NA21 (Production) and CS32 (Sandbox) (there may be other instances they're found on). In case you are trying to connect Marketing Cloud with Salesforce Government Cloud. Please log a case with Marketing Cloud Support to assist you in resolving the Error: "An exception occurred while saving the integration".

 Scenario 8: Forward-to-a-Friend Subscriber List

There is a potential issue that the Forward-to-a-Friend Subscriber List will be missing in the Salesforce Integration configuration page within Setup in the Marketing Cloud, despite the FORWARD_TO_FRIEND Business Rule being enabled.

STEPS TO REPRODUCE:

• Go to Setup
• Navigate to Platform Tools > Apps > Salesforce Integration
• Notice the Forward-to-a-Friend Subscriber List is blank
• Try to connect the account
• Receive an error indicating "An exception occurred while saving the integration"

Please log a case with Marketing Cloud Support to assist you in resolving the Error: "An exception occurred while saving the integration".