The way I have used, and had success with, is close WinPMail. Then rename heirarch.pm to heirarch.pm.bak. Then restart WinPMail and all folder file pairs should be recognized again. Any tray structure, if you had any, will be gone and need to be recreated.

 What I like to do, if all is well, just "in case" routinely save a .bak copy of heirarch, state and the pmail.ini files before they are needed. I go years at a time without ever having to restore anything, but if there is ever a problem I feel better knowing those .bak files are available.

I have a folder, FOLD3571, that has been around forever, with 100s of messages.  Both the .pmi and .pmm are on the hard drive. But suddenly the folder is not recognized among Pegasus' folders.  State shows it as "67AE44A6:5390:FOLD3571=197,101,668,459,"184,250,272,0,682,0"   Hierarch.pm shows it as "0,0,"67AE44A6:5390:FOLD3571","2DC36587:My mailbox",Name_Unavailable"
 How do I 'reattach' it?