I am experiencing a similar problem, and possibly may have narrowed down its cause.
In one instance when I run either TARSAV or TARCON (same as TARSAV except it does not write the DSK: specification to the tape) I get an "insufficient free memory" message after writing approximately 2,940 files and 43,647 blocks. I have rebooted the Alpha, run this save on different tapes (both 525MB and 4GB), and run it with 1.3MB of memory as well as 26MB; all with the same "insufficient free memory" message.
I ran a second save of 10,145 files in 39,217 blocks and it ran fine.
I ran a third save of 740 files in 680,383 blocks and it also ran fine.
The one difference I see is that in the save that failed I manually specified 17 different device specs (ie TARSAV ALA0:[],ALX0:[],BBC0:[],CXP0:[], etc) and it aborted while saving approx the 12th device. The two saves that worked (one with thousands more files and the other with many more blocks) were both of a singe device spec (and BIG0:[] was obviously of an extended directory).
Were your saves that failed also of a large number of device specs ?
Don't know if this might help Jack or not ? Since my one test will fail every time I can certainly test any beta patch that Jack might offer.
FYI my versions are:
TARRES LIT 4 2.0(100)
TARCON LIT 11 2.0(107)
TARDIR LIT 2 1.0(104)
TARSAV LIT 11 2.0(106)
TARSER LIT 2 1.0(101)