First of all Yamaha Premium packs are encrypted so that they will only load on the very keyboard that they were purchased for, so if the packs were purchased for a different Tyros4, they won't load on yours!
If the packs actually are for your specific Tyros4, have you checked that you have enough space on the Expansion Memory Module fitted to your keyboard for the packs/voices?
If you do have space on the Expansion Memory board, your problem may be because your keyboard's User drive is full or almost full.
Although any new wave samples used by an expansion voice are stored on the Expansion Memory Module, each voice also requires a small amount of space on the User drive.
You can check the amount of space on the User drive if you open a file selection window (Styles for example), tab to 'USER' and switch to the alternate List view by pressing 'VIEW' (upper #7 button). In the List View press 'PROPERTY' (F button) and a window will pop up showing 'ALL SIZE : 5.95 (MBytes)', which is the total size of the User drive, and 'FREE AREA : n.nn (MBytes)', which is the amount of remaining space.
If the Free Area figure is very small, this is likely to be the cause of your problem and you will need to clear some space on the User drive to load all of your expansion voices.
If the above is not the cause of the problem, the Operating System imposes a limit on certain parameters associated with managing the wave samples for expansion voices, and once these limits have been exceeded, no more waves can be added even if there is plenty of empty space on the Expansion board!
The most problematic of these limits, and the one that many people encounter is the so called 'Wave Count' which is limited to 9999 in the latest version of the firmware (ver. 1.10). It was limited to 8192 in earlier firmware versions.
To check this and the other parameters associated with the expansion memory, press 'Voice Creator' > 'Expansion Module' > 'Property' (lower 7 or 8 button). The display that opens will show the Wave Count and the rest of the parameters including the remaining space. If any of these are almost fully used up, this could prevent you from loading further voices.
Regards
Ian