Hello!
To increase the memory allocation to MRJ just highlight the original application icon and then from the File Menu select Show Info then from the submenu select memory. Here increase the maximum setting(but dont touch the minimum settings) the maximum should be set to 32000. Then re-start your computer for the changes to take effect. Now try to Launch LW and see if it works. By the way in which way did you install MRJ. One common mistake is to accept the LW installers question that it has a newer version of MRJ included and it asks you if you want the installer to install that too. You should refuse that offer. Instead you should download the MRJ installer from here and install it using its installer. For some reason the LW installer has never been good at installing MRJ for you. Here is the link:
MRJ 2.2.5