I was exactly in the same problem, with several DTSs, all of them with at least 1 FTP-Task.
I wanted to put in production(SQL2KSP4) the new DTSs, which were working fine on QA(SQL2KSP4). First I tried several attempts to save them from the QA server registered in the SQL Enterprise Manager of my PC; the Saving process to the production server worked fine but when I wanted to open any of them, the 'Unspecified error' appeared. Then I tried using the DTSBackup2000 utility, but didn't work either. So, I connected to the production server using Terminal Services, then I register the QA server in the SQL Enterprise Manager and transferred all the packages to the new server (at that time 'local' server), and this way I could open all of them, make them any change, save it, and reopen it again perfectly.
Warning: The issue was still in the environment, cause any additional change to the DTS, I have to make it directly in the production server using TermServ. If I change the DTS from my PC, the DTS get crashed again. At least this way I accomplished the task of put it in production. Hope this help someone.