Accessing to rat dataset is unstable during last few days. Sometimes it works, sometimes I get error like the following (R code):

library(biomaRt)
human = useEnsembl("ENSEMBL_MART_ENSEMBL", dataset = "hsapiens_gene_ensembl") # works fine
rat = useEnsembl("ENSEMBL_MART_ENSEMBL", dataset = "rnorvegicus_gene_ensembl") # Error!
Error in checkDataset(dataset = dataset, mart = mart) : 
  The given dataset:  rnorvegicus_gene_ensembl , is not valid.  Correct dataset names can be obtained with the listDatasets() function.

Update: Problem seems gone after I updated all bioconductor packages to 3.6. Will come back if it happens again.

Here is session info. I also tried yesterday with biomartian and faced the same problem.

sessionInfo() R version 3.4.4 (2018-03-15) Platform: x86_64-pc-linux-gnu (64-bit) Running under: Ubuntu 16.04.4 LTS

Matrix products: default
BLAS: /usr/lib/openblas-base/libblas.so.3
LAPACK: /usr/lib/libopenblasp-r0.2.18.so

locale:
 [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C               LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8     LC_MONETARY=en_GB.UTF-8   
 [6] LC_MESSAGES=en_GB.UTF-8    LC_PAPER=en_GB.UTF-8       LC_NAME=C                  LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C       

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

other attached packages:
[1] biomaRt_2.34.2       AnnotationHub_2.10.1 BiocGenerics_0.24.0  vimcom_1.2-5         setwidth_1.0-4       colorout_1.1-0      

loaded via a namespace (and not attached):
 [1] SummarizedExperiment_1.8.1    progress_1.2.0                lattice_0.20-35               htmltools_0.3.6               stats4_3.4.4                 
 [6] rtracklayer_1.38.3            yaml_2.1.19                   interactiveDisplayBase_1.16.0 blob_1.1.1                    XML_3.98-1.11                
[11] rlang_0.2.1                   later_0.7.3                   DBI_1.0.0                     BiocParallel_1.12.0           bit64_0.9-7                  
[16] matrixStats_0.53.1            GenomeInfoDbData_1.0.0        stringr_1.3.1                 zlibbioc_1.24.0               Biostrings_2.46.0            
[21] memoise_1.1.0                 Biobase_2.38.0                IRanges_2.12.0                httpuv_1.4.4.2                GenomeInfoDb_1.14.0          
[26] BiocInstaller_1.28.0          AnnotationDbi_1.40.0          Rcpp_0.12.17                  xtable_1.8-2                  promises_1.0.1               
[31] DelayedArray_0.4.1            S4Vectors_0.16.0              XVector_0.18.0                mime_0.5                      bit_1.1-14                   
[36] Rsamtools_1.30.0              hms_0.4.2                     digest_0.6.15                 stringi_1.2.3                 shiny_1.1.0                  
[41] GenomicRanges_1.30.3          grid_3.4.4                    tools_3.4.4                   bitops_1.0-6                  magrittr_1.5                 
[46] RCurl_1.95-4.10               RSQLite_2.1.1                 crayon_1.3.4                  pkgconfig_2.0.1               Matrix_1.2-14                
[51] prettyunits_1.0.2             assertthat_0.2.0              httr_1.3.1                    rstudioapi_0.7                R6_2.2.2                     
[56] GenomicAlignments_1.14.2      compiler_3.4.4