Top Secret 'FACILITY' Control Options suboption SIGN determines if multiple signons are allowed. SIGN(S) only allows a single signon. SIGN(M) allows multiple signons.
In your Top Secret parameter file, set the following: FAC(CICSPROD=SIGN(M)) and recycle the TSS partition or IPL for the changes to go into effect. SIGN(M) is documented in the Top Secret Control Options Guide.