Opening an RFC Connection (CPIC-CALL) with STMS

When I am trying to import the transports from sap Quality system it is showing the below error. Please help me to troubleshoot the error. 

RFC communications error with system/destination email@removed _DEV 
Message no. XT101 

Diagnosis 
An RFC error occurred in the TMS communications layer. 

Target system: PRD.DOMAIN_DEV(100) 
Function: TMS_TP_SHOW_BUFFER 
RFC message: Error when opening an RFC connection (CPIC-CALL: ' 

System Response 
The function terminates.