I have encountered an error I couldn't find on the help page and the vignette:

string_db$plot_ppi_enrichment(string_id$STRING_id,
                      title = paste("Interaction enrichment of", moduleName))
Error in (function (classes, fdef, mtable)  :
  unable to find an inherited method for function ‘nodes’ for signature ‘"igraph"’
Calls: sapply ... ppie.getNumEdgesBetween -> unlist -> neighborhood -> nodes -> <Anonymous>
Execution halted

I could successfully plot other groups of proteins, this one is however one of the biggest I have plotted it has 358 proteins and 2270 interactions according to the following code, which ran correctly:

string_db$plot_network(string_id$STRING_id, # payload_id = payload,
                           add_link = FALSE)

After further exploring the issue I found that:

tryCatch({string_db$plot_ppi_enrichment(string_id$STRING_id,
                      title = paste("Interaction enrichment of", moduleName))},
             error = function(e) {
               message("Couldn't map the enrichment of STRING")
               sessionInfo()
               message(e)
             })

|=================================                                     |  47%Couldn't map the enrichment of STRING

unable to find an inherited method for function ‘nodes’ for signature ‘"igraph"’Analyzing purple module!
'select()' returned 1:1 mapping between keys and columns
Warning:  we couldn't map to STRING 3% of your identifiers
ERROR: We do not support lists with more than 400 genes.
Please reduce the size of your input and rerun the analysis.     
Error in get_png(string_ids, payload_id = payload_id, required_score = required_score)

If there is an error why is still the get_png method called? Why can it work with 358 proteins if the limit is 400? Which is this file which is being downloaded as implied with the "|  47%" ? Why I can't create graphs bigger than 400?

My session:

R version 3.2.3 (2015-12-10)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 14.04.2 LTS

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=es_ES.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=es_ES.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=es_ES.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=es_ES.UTF-8 LC_IDENTIFICATION=C       

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

other attached packages:
 [1] STRINGdb_1.10.1    hash_2.2.6         gplots_3.0.1       RColorBrewer_1.1-2
 [5] plotrix_3.6-2      RCurl_1.95-4.8     bitops_1.0-6       igraph_1.0.1      
 [9] plyr_1.8.4         sqldf_0.4-10       RSQLite_1.0.0      DBI_0.4-1         
[13] gsubfn_0.6-6       proto_0.3-10       png_0.1-8         

loaded via a namespace (and not attached):
[1] Rcpp_0.12.5        gtools_3.5.0       chron_2.3-47       magrittr_1.5      
[5] KernSmooth_2.23-15 gdata_2.17.0       caTools_1.17.1     tcltk_3.2.3