There are just 'normal' messages seen on any ASA/PIX/FWSM, ignore them.
(I think) they occur because the firewall has already closed the connection (or at least one TCP end-point has) and the other side still is trying to 'finish' the connection. And since its not in the state table of the firewall its denied, hence the (no connection).
From the official docs:
Error Message %PIX|ASA-6-106015: Deny TCP (no connection) from IP_address/port to
IP_address/port flags tcp_flags on interface interface_name.
Explanation The security appliance discarded a TCP packet that has no associated connection in the security appliance's connection table. The security appliance looks for a SYN flag in the packet, which indicates a request to establish a new connection. If the SYN flag is not set, and there is not an existing connection, the security appliance discards the packet.
Recommended Action None required unless the security appliance receives a large volume of these invalid TCP packets. If this is the case, trace the packets to the source and determine the reason these packets were sent.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...