untar() error

Dear List,

I have a list of 600+ *.gz files that I would like to extract and read the
geotiffs contained within them. I tried using the untar() function to
simplify this task but I am stumped by an error. I've combed the Internet
for a solution without luck. The details are below, and any help in solving
this matter is appreciated.

files = list.files(path = "J:/GIMMS/NDVI", pattern = "data.tif.gz",

all.files = TRUE, full.names = TRUE, recursive = TRUE, ignore.case = TRUE,
include.dirs = TRUE)

lapply(files, untar)

Error in rawToChar(block[seq_len(ns)]) :
   embedded nul in string: 'II*\0?? <\001??
\0\0`G\0\0\fn\0\0?????\0\0d??\0\0\020??\0\0??\b\001\0h/\001\0\024V\001\0??|\001\0l??\001\0\030??\001\0????\001\0p\027\002\0\034>\002\0??d\002\0t???\002\0
??\002\0????\002\0x??\002\0$&\003\0??L\003\0|s\003'

untar(files[1])

Error in rawToChar(block[seq_len(ns)]) :
   embedded nul in string: 'II*\0?? <\001??
\0\0`G\0\0\fn\0\0?????\0\0d??\0\0\020??\0\0??\b\001\0h/\001\0\024V\001\0??|\001\0l??\001\0\030??\001\0????\001\0p\027\002\0\034>\002\0??d\002\0t???\002\0
??\002\0????\002\0x??\002\0$&\003\0??L\003\0|s\003'

untar("J:/GIMMS/NDVI/1981/81aug15a.n07-VIg/81aug15a.n07-VIg_data.tif.gz")

Error in rawToChar(block[seq_len(ns)]) :
   embedded nul in string: 'II*\0?? <\001??
\0\0`G\0\0\fn\0\0?????\0\0d??\0\0\020??\0\0??\b\001\0h/\001\0\024V\001\0??|\001\0l??\001\0\030??\001\0????\001\0p\027\002\0\034>\002\0??d\002\0t???\002\0
??\002\0????\002\0x??\002\0$&\003\0??L\003\0|s\003'

traceback()

3: rawToChar(block[seq_len(ns)])
2: untar2(tarfile, files, list, exdir)
1: untar(files[1])

sessionInfo()

R version 2.15.2 (2012-10-26)
Platform: x86_64-w64-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United
States.1252    LC_MONETARY=English_United States.1252 LC_NUMERIC=C

[5] LC_TIME=English_United States.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base