Running examples in 'cowplot-Ex.R' failed
The error most likely occurred in:

> ### Name: add_sub
> ### Title: Add annotation underneath a plot
> ### Aliases: add_sub
> 
> ### ** Examples
> 
> p1 <- ggplot(mtcars, aes(mpg, disp)) + geom_line(colour = "blue") + background_grid(minor='none')
> ggdraw(add_sub(p1, "This is an annotation.\nAnnotations can span multiple lines."))
> 
> # You can also do this repeatedly.
> p2 <- add_sub(p1, "This formula has no relevance here:", y  = 0, vjust = 0)
> p3 <- add_sub(p2, expression(paste(a^2+b^2, " = ", c^2)))
> ggdraw(p3)
> 
> #This code also works with faceted plots:
> plot.iris <- ggplot(iris, aes(Sepal.Length, Sepal.Width)) +
+   geom_point() + facet_grid(. ~ Species) + stat_smooth(method = "lm") +
+   background_grid(major = 'y', minor = "none") + # add thin horizontal lines
+   panel_border() # and a border around each panel
> p2 <- add_sub(plot.iris, "Annotation underneath a faceted plot, left justified.", x = 0, hjust = 0)
Error in namespaceExport(ns, exports) : 
  undefined exports: %s!=%, %s!==%, %s+%, %s<%, %s<=%, %s==%, %s===%, %s>%, %s>=%, %stri!=%, %stri!==%, %stri+%, %stri<%, %stri<=%, %stri==%, %stri===%, %stri>%, %stri>=%, stri_datetime_add<-, stri_sub<-, stri_subset<-, stri_subset_charclass<-, stri_subset_coll<-, stri_subset_fixed<-, stri_subset_regex<-, stri_c, stri_c_list, stri_cmp, stri_cmp_eq, stri_cmp_equiv, stri_cmp_ge, stri_cmp_gt, stri_cmp_le, stri_cmp_lt, stri_cmp_neq, stri_cmp_nequiv, stri_compare, stri_conv, stri_count, stri_count_boundaries, stri_count_charclass, stri_count_coll, stri_count_fixed, stri_count_regex, stri_count_words, stri_datetime_add, stri_datetime_create, stri_datetime_fields, stri_datetime_format, stri_datetime_fstr, stri_datetime_now, stri_datetime_parse, stri_datetime_symbols, stri_detect, stri_detect_charclass, stri_detect_coll, stri_detect_fixed, stri_detect_regex, stri_dup, stri_duplicated, stri_duplicated_any, stri_enc_detect, stri_enc_detect2, stri_enc_fromutf32, stri_enc_get, stri_enc_inf
Calls: add_sub ... tryCatch -> tryCatchList -> tryCatchOne -> <Anonymous>
Execution halted