INDX tablespace in increasing

[minal_yawale]

Yesterday i fired following qury to rebuild index:
alter index index_name rebuild ONLINE
Then i got these errors:
ERROR at line 1:
ORA—01652: unable to extend tenp segnent by 256 in tablespace TEMP
ORA—27059: skqfrsz: could not reduce file size
OSD—O4005: SetrilePointer() failure, unable to read fron file
0/S—Error: (05 112) There is not enough space on the disk.

My temporay tablespace is 2 GB and free space in index tablespace is 40 GB and the index is of 10 GB.
But free space on the drive where temp01.dbf is reside is 760 kb . but before tht i've removed 4 GB of datafiles to another drive. Still its showing 760 KB. Why it is so? I will add tempfile to tht temp tablespace to anothr drive and will try again.
Now if i give command
alter index index_name rebuild unrecoverable tablespace indx, then whether it will give me same error?thanks in advance.