the serial ports on the MX and MXE controllers are VERY fragile.... the LEAST bit of static electricity will usually pop them.. and the port may very well send out to you but not receive.. thats a common issue...
I have also had on 7.0 variants an issue where the system would boot and run but not allow login through the ESM..., however telnetting to it to the SX-2000 call control shell and then running a dbms check full... then rebooting resolved the issue... tech support indicated the database corrupted and caused the issue...
also, unlike the sx-2000, on the 3300 if you get a corrupted database you are not totally hosed...doing a backup and restore forces a database "cleaning" which will get rid of the corrupted parts of your database and load the good part... so you may lose a couple stations or a Class of service etc but not the whole DB...
those familiar with SX-2000 database Loss find this a real nice "feature"...
-Christopher