Calling RFC and getting ABAP dump when maximum GUI sessions reached in sap

Hi ,

Please help on this.

Calling a RFC in a standard program and it is causing ABAP dump when maximum sessions reached. If a session is available, occurred no issue. Pleas help me to get solution.

Sample code:
CALL FUNCTION 'Z_SALES_ORDER_CHANGE' STARTING NEW TASK 'TSK1' DESTINATION 'NONE' PERFORMING return_info ON END OF TASK

EXPORTING

i_vbeln = lwa_vbap2-vbeln

TABLES

it_sales_order = lit_sales_tmp .

IF sy-subrc = 0.

WAIT UNTIL functioncall ='X'.

IMPORT lit_return2[] FROM MEMORY ID 'ABC'.

functioncall = space.

ENDIF.

FORM RETURN_INFO using tsk1 TYPE any.

RECEIVE RESULTS FROM FUNCTION 'Z_SALES_ORDER_CHANGE'
TABLES
IT_SALES_ORDER = lit_sales_tmp
functioncall = 'X'.

ENDFORM. " RETURN_INFO