Hello, I'm running biomaRt as follow, to retrieve rs IDs with providing SNPs chromosome number and position

ensembl = useMart(biomart = "ENSEMBL_MART_SNP", host = "grch37.ensembl.org", path = "/biomart/martservice",dataset = "hsapiens_snp") 

getBM(attributes = c("refsnp_id", "chr_name", "chrom_start", "chrom_end", "allele", "allele_1", "minor_allele", "minor_allele_freq", "chrom_strand"), 
    filters = "chromosomal_region", 
    values = chrpos_rsidNA, 
    mart = ensembl)

head(chrpos_rsidNA)
[1] "21:14714623:14714623" "21:14756926:14756926" "21:14760841:14760841"
[4] "21:14802991:14802991" "21:15471360:15471360" "21:15535590:15535590"

I get the following error message

Error in getBM(attributes = c("refsnp_id", "chr_name", "chrom_start",  : The query to the BioMart webservice returned an invalid result: biomaRt expected a character string of length 1. 
Please report this on the support site at http://support.bioconductor.org


> sessionInfo()
R version 3.5.1 (2018-07-02)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.1 LTS

Matrix products: default
BLAS: /home/R/R-3.5.1/lib/R/lib/libRblas.so
LAPACK: /home/R/R-3.5.1/lib/R/lib/libRlapack.so

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

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

other attached packages:
[1] bindrcpp_0.2.2    biomaRt_2.38.0    dplyr_0.8.0.1     data.table_1.12.0

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.0           pillar_1.3.1         compiler_3.5.1      
 [4] bindr_0.1.1          prettyunits_1.0.2    bitops_1.0-6        
 [7] tools_3.5.1          progress_1.2.0       digest_0.6.18       
[10] bit_1.1-14           RSQLite_2.1.1        memoise_1.1.0       
[13] tibble_2.0.1         pkgconfig_2.0.2      rlang_0.3.1         
[16] DBI_1.0.0            curl_3.3             parallel_3.5.1      
[19] xml2_1.2.0           httr_1.4.0           stringr_1.4.0       
[22] S4Vectors_0.20.1     IRanges_2.16.0       hms_0.4.2           
[25] stats4_3.5.1         bit64_0.9-7          tidyselect_0.2.5    
[28] glue_1.3.0           Biobase_2.42.0       R6_2.4.0            
[31] AnnotationDbi_1.44.0 XML_3.98-1.18        purrr_0.3.1         
[34] blob_1.1.1           magrittr_1.5         BiocGenerics_0.28.0 
[37] assertthat_0.2.0     stringi_1.3.1        RCurl_1.95-4.12     
[40] crayon_1.3.4

Thanks