KB234437: "Error fetching the list of reports from the external source" display when access Salesforce.com reports in Microstrategy Web Data Import

SYMPTOM
In Strategy Web 9.3.0 and higher, when fetching report from Salesforce.com using data import feature, user get following error message:

Uh-Oh, Error fetching the list of reports from the external source

 
As shown in below image:

 
For more information regarding configuring Salesforce.com for importing data, refer to below Technical Note:
KB42459: How to import data from Salesforce in MicroStrategy Web 9.4.1 and 9.5.x
 
In DssErrors log, entries like below could be found: 

[Database Classes][Error] mstr-rest: post() failed. HTTP error encountered while trying to access a REST service. 
Error type: XQuery Engine error. couldn't connect to host. Connection String: XQUERY;SERVER_URL=https://ap1.salesforce.com;MULTITHREAD;. Connection String: XQUERY;SERVER_URL=https://ap1.salesforce.com;MULTITHREAD;.

[Kernel][Error][0x8004180E] Error in accessing information from the external data source (Database Instance: null, Error: mstr-rest: post() failed. HTTP error encountered while trying to access a REST service. Error type: XQuery Engine error. couldn't connect to host. Connection String: XQUERY;SERVER_URL=https://ap1.salesforce.com;MULTITHREAD;.)

 
 
CAUSE:
One of the possible cause for this issue is firewall in Intelligence Server machine blocks the communication between Intelligence Server and Salesforce.
 
ACTION:
Allow communication between Intelligence Server and Salesforce.com in Firewall.