[R] as.POSIXct problem?

[Frank E Harrell Jr]

Under

platform i686-pc-linux-gnu
arch     i686             
os       linux-gnu        
system   i686, linux-gnu  
status                    
major    1                
minor    6.1              
year     2002             
month    11               
day      01               
language R                

> x <- strptime(c('10/10/1969','12/31/2002'),format='%m/%d/%Y')
> x
[1] "1969-10-10" "2002-12-31"
> as.POSIXct(x)
[1] NA               "2002-12-31 EST"

Why the NA?  If this is not the preferred way to convert a character string to POSIXct what is?  On a more minor note why the EST if no time is printed?

Thanks,

Frank
-- 
Frank E Harrell Jr              Prof. of Biostatistics & Statistics
Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences
U. Virginia School of Medicine  http://hesweb1.med.virginia.edu/biostat