[R] Specifying interactions in rms package... error

[Rob James]

I am encountering an error I do not know how to debug. The error arises 
when I try to add an  interaction term involving two continuous 
variables (defined using rcs functions) to an existing (and working) model.

The new model reads:

  model5 <- lrm( B_fainting ~   gender+  rcs(exactage, 7) +  
rcs(DW_nadler_bv, 7) +           rcs(drawtimefrom8am, 7)+  DW_firsttime+ 
   DW_race_eth +
  rcs(DW_BPS, 5)+  rcs(DW_BPD, 5)+  rcs(pulse3, 5)+  locat2+
(rcs(exactage, 3) * rcs(drawtimefrom8am, 3))
   )

This gives rise to the following error:

----
Error in dimnames(X)[[2]] <- atr$colnames :
   length of 'dimnames' [2] not equal to array extent
In addition: Warning message:
In names(nmiss)[jz] <- fname[asm != 9] :
   number of items to replace is not a multiple of replacement length
----

The sessionInfo() output is below, but I think relatively unremarkable.  
The dataset is very large (about 550K observations, although the outcome 
(B_fainting)  is relatively sparse with only 1500 events in this 
sample.   I do not get this error when the interaction term is replaced 
by two categorical variables (data not shown).  I can replicate this 
error when there is just one continuous variable and one categorical 
variable.


I'd welcome suggestions. Thank you in advance.





sessionInfo()
R version 2.11.0 (2010-04-22)
x86_64-pc-linux-gnu

locale:
  [1] LC_CTYPE=en_CA.UTF-8       LC_NUMERIC=C               
LC_TIME=en_CA.UTF-8
  [4] LC_COLLATE=en_CA.UTF-8     LC_MONETARY=C              
LC_MESSAGES=en_CA.UTF-8
  [7] LC_PAPER=en_CA.UTF-8       LC_NAME=C                  LC_ADDRESS=C
[10] LC_TELEPHONE=C             LC_MEASUREMENT=en_CA.UTF-8 
LC_IDENTIFICATION=C

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

other attached packages:
[1] gmodels_2.15.0  rms_3.0-0       Hmisc_3.8-2     survival_2.35-8 
odfWeave_0.7.14 XML_3.1-0
[7] lattice_0.18-8

loaded via a namespace (and not attached):
[1] cluster_1.13.1 gdata_2.8.0    grid_2.11.0    gtools_2.6.2   MASS_7.3-7