[R] text miner error: Error in UseMethod("meta", x)

[Sun Shine]

Hi list

I've been working my way through a tutorial on text mining ( 
http://onepager.togaware.com/TextMiningO.pdf ) and all was well until I 
came across this problem using tm (text miner):

++++++++++code+++++++++++++++++++
 > docs <- tm_map(docs, content_transformer(tolower))
Warning messages:
1: In mclapply(x$content[i], function(d) tm_reduce(d, x$lazy$maps)) :
   all scheduled cores encountered errors in user code
2: In mclapply(content(x), FUN, ...) :
   all scheduled cores encountered errors in user code
++++++++++end-code++++++++++++++++

After some searching, it appears the best fix for this problem was to 
pass an explicit lazy=TRUE argument to tm, like this:

 > docs <- tm_map(docs, content_transformer(tolower), lazy=TRUE)

However, a little further on in the tutorial to set up the text matrix, 
a related (?) error was returned:

++++++++++code+++++++++++++++++++
 > dtm <- DocumentTermMatrix(docs)
Error in UseMethod("meta", x) :
   no applicable method for 'meta' applied to an object of class "try-error"
In addition: Warning message:
In mclapply(unname(content(x)), termFreq, control) :
   all scheduled cores encountered errors in user code
++++++++++end-code++++++++++++++++

I tried applying the explicit lazy=TRUE again, but doesn't change 
things. I have gone over the tutorial again and have followed all of the 
steps (including loading the requisite libraries). Moreover, searching 
on the web seems to return several contradictory suggestions and I'm no 
wiser than I was before.

The closest I came to an answer was at Stack Overflow 
http://stackoverflow.com/questions/24771165/r-project-no-applicable-method-for-meta-applied-to-an-object-of-class-charact 
and that answer suggested using the latest tm (v 0.6) and claimed that 
the earlier tolower step was wrong. However, my code used the 
recommended: corpus <- tm_map(corpus, content_transformer(tolower))

Is there anyone on the list who could either sign-post me to a solution 
or assist in debugging this please?

I'm running R version 3.1.2 and tm is 0.6

Many thanks

Sun