Mbox cannot start new session or load in old sessions.

Session Must Be On An Audio Record Volume Means You Do Not Have Protools Program, Session Files, Audio Files Installed And Set To Record On The Main Hard Drive Or A Hard Drive That Has Be Formated With A Volume .  Un-Install Then Re-Install Protools Software And Make Sure The Programs And All Files Are Written To The Main Hard Drive .  When You Open Protools Files Or Older Version Protools Files That Are Not On The Main Hard Drive You Need To Copy And Paste The Session With All Audio Files To The Same Hard Drive As The Program Before Opening Them .  If You Plan To Record, Mix, Master On A Previous Protools Session I Suggest The Session To Be On The Main Hard Drive .  One Thing To Do In Order To Prevent Protools From Recording To Back Up Hard Drives Or Media Disc Is To Create A New Session As Soon As You Get Protools Up And Running, Make Sure The Session Is Created/Saved Into The Main Hard Drive .  Do Not Open Previous Sessions That Are Save To Other Hard Drives/Media The First Time You Get The Protools Installed .  Protools Can Record On External Hard Drives ( Firewire Recommended ) But Work Better With A Internal Hard Drive With at least 7200 RPM And 8 MB Cache .  Hard Drive, Cables, And Port Strength/Compatibility Have A Lot To Do With Weather Or Not A External Drive Is Best For Recording .  To Repair, Format, And Set Your Hard Drive With A Volume Go To Disk Utility Under Utility Located In The Applications Folder .  Reformatting Or Repairing A Internal/External Hard Drive Will More Then Likely Erase The Whole Hard Drive So Make Sure U Back Up All Files To A Hard Drive/Media To Save All Information .  I Hope This Helps You Out A Lot .  Thanks .

Digidesign website had the answer....go to windows,show workspace and change the settings for your relevant disc from transfer T to R...record in the A..audio column.
Thanks  Bobcat8