([0-9]|[0-9][0-9])
The parenthesis are there because of the or. The expression matches either 1 or 2 numbers, but not more.
VOIP/ten_gig_block_kc705/core_reset_dly_reg\[[0-9]\]_srl3__VOIP_ten_gig_block_kc705_core_reset_dly_reg _p_([0-9]|[0-9][0-9])/D
There is a space between "VOIP/ten_gig_block_kc705/core_reset_dly_reg\[[0-9]\]_srl3__VOIP_ten_gig_block_kc705_core_reset_dly_reg" and "_p_([0-9]|[0-9][0-9])/D"
The net may also have a different name in you design, or a different full hierarchy.