In certain situations, it's possible to receive an 'Out of PGM/MEM' message when loading an existing DAW session that uses a UAD plug-in that requires a lot of PGM resources, such as the Ocean Way or AKG BX20 plug-ins - in these sessions, the plug-in will have loaded correctly into the project originally but the message will appear after closing and reopening the session.
This happens due to the nature of how most DAWs load plug-ins when recalling a session. For example, the Ocean Way plug-in uses ~75.6% of the PGM resources of a single SHARC chip which cannot be split up among multiple chips, meaning that one of your SHARC chips must have this much PGM available to load the plug in. When loading the plug-in into a session in real time, the UAD system will automatically reallocate the currently loaded plug-ins to make room for the Ocean Way, however when you recall a DAW session the plug-ins aren't loaded in the same efficient manner - most DAWs will simply load the plug-ins in the order that they appear in your session left to right and will not reallocate plug-ins to different SHARC chips to get the most out of the available resources. This means that if you have a bunch of tracks with UAD plug-ins farther left in your mix window then the track that the Ocean Way plug-in is loaded to, the other UAD plug-ins will load first and there may not be 75.6% of PGM resources available on a single SHARC chip after all of these plug-ins are loaded.
Since most DAWs load plug-ins in the order they appear left to right when reopening a session, the solution is to open the Mixer view in your DAW and drag the track containing the offending UAD plug-in all the way to the far left of your screen (or to the top of the project if in Edit / linear view), so that the track containing the plug-in is the first track in the project - this will cause that particular plug-in to load first, and then all other plug-ins (which most likely use less resources) will be loaded after. This should allow you to close and reopen these sessions without receiving the 'Out of DSP/PGM' message.