Salesforce: Can't refresh access token. Response:

{"error":"invalid_grant","error_description":"token validity expired"}

Sometimes we may not be able to refresh the Salesforce access_token using the rest api and get below error in logs

28.03.2017 23:41:40.184 *ERROR* [0:0:0:0:0:0:0:1 [1490724696957] GET /content/training/en/salesforce/jcr:content/par/salesforcesearch.html HTTP/1.1] com.adobe.cq.mcm.salesforce.SalesforceClient Can't refresh access token. Response: {"error":"invalid_grant","error_description":"token validity expired"}

Root cause:
This issue is due to the "Refresh Token Policy" settings of the connected app is set to "Immediately expire refresh token"

Follow the below steps to resolve this issue:
Goto setup -> Connected apps ->Manage Policies
Select Refresh Token Policy as Refresh token is valid until revoked