You say about 40-45 nat ip's and clients. Are there more clients then ip's? Do you have nat overload configured. The license controls which features you have. For example, if you had a 501 restriceted this would be a problem.
Say you have 40 ip's in NAT and 41 pc's. All tried to connect then the 41st would not be able to until the xlate time out and freed an IP. With nat overload (PAT) this would take care of this issue. See link.
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...