Due to the number of different processes and options available within ACEmessage it is useful to understand the process of ACE Client deciding to display a message. Occasionally you may have sent a message and wondered why it did not display on the target desktop. This article will detail that process in order for you to troubleshoot the issue and also discuss some of the common causes.
This article assumes that the message has been successfully sent to the ACE Client. You will often see a screenshot like the below to verify this (In the default Unicast Message Delivery Mode):

As you can see from the above, ACEmessage is reporting that the message was successfully sent to the computer COMP_1110. It is important to understand that this success is reporting the Sending of the message, not the display of the message.
As per the above example, the computer COMP_1110 has received the message over the network. The process which occurs on the above ACE Client computer is:

There are two common reasons why a message is successfully sent and not displayed (They are also identified in the above flow chart).
All of these reasons are easily rectified. Double check your Target List in your original Sent Message. Make sure that the User/Computer you are targeting would PASS one of the targets listed. This is a simple cause of many 'not displayed' messages. You will also need to check if you have an ACEmessage Authorised domain group in your Active Directory domain. If this group exists then the ACEmessage sending User or Computer Account MUST be listed in this Group. If it is not listed then your message will not be considered to be from an authorised source.
It is possible to see how ACE Client is processing a message once received. If you follow the below article, it will explain how to enable ACE Client Error Logging.
Enable Error Logging on ACE Client
If you enable error logging on ACE Client as per the above article link, then send your message to the ACE Client. You will be able to open the ACE Client Debug.log file (As per the article) and review the plain text english processing which ACE Client does when it receives a new message. Simply look for the section:
************ MSG RECEIVED ************
Below the MSG RECEIVED area you will see the message being loaded and the above flow chart being followed. The Log File can often point to why your message is not being displayed, for example the above Common Reasons are listed in the ACE Client Debug.log file as:
So reviewing the ACE Client Debug.log file can really help in tracking down why your message is not being displayed.
On the above date a problem was identified which can cause a client computer not to display a message. This is fully documented in the following article: Error: The path is not of a legal form