Simp
ArchiveExplorerUI.asp is not supported on MAC.
It's supported on Internet Explorer, only.
-> ftp://exftpp.symantec.com/pub/support/products/Exchange_Mailbox_Archiving_Unit/276547.pdf
-> Page 18
FireFox and Safari are currently PENDING certification, and currently NOT supported.
What is your C: Drive used for? I think 116 GB should be enough.
Your Index drive however is probably not large enough.
Depending on your settings, you can have brief (8%) medium (12%) and full (20%) index Size.
Standard setting is medium, I believe, which would lead to ~500 GB Index.
Cheers
Michel