Error(s) in re-building vignettes:
  ...
duplicated vignette title:
  ‘Retrieving and Analyzing PubMed Records via easyPubMed’

--- re-building ‘easyPM_vignette_html.Rmd’ using rmarkdown
Quitting from lines 39-50 (easyPM_vignette_html.Rmd) 
Error: processing vignette 'easyPM_vignette_html.Rmd' failed with diagnostics:
1: Input is not proper UTF-8, indicate encoding !
Bytes: 0xF0 0x33 0xC2 0x96
2: Opening and ending tag mismatch: Citation line 784 and Reference
3: expected '>'
4: Opening and ending tag mismatch: ReferenceList line 746 and PubmedData
5: Opening and ending tag mismatch: PubmedData line 704 and PubmedArticle
6: PCDATA invalid Char value 16
7: Opening and ending tag mismatch: Reference line 2009 and ArticleIdList
8: Opening and ending tag mismatch: ReferenceList line 1918 and Reference
9: Opening and ending tag mismatch: PubmedData line 1871 and ReferenceList
10: Opening and ending tag mismatch: PubmedArticle line 1589 and PubmedData
11: PCDATA invalid Char value 1
12: PCDATA invalid Char value 29
13: PCDATA invalid Char value 23
14: PCDATA invalid Char value 2
15: PCDATA invalid Char value 4
16: PCDATA invalid Char value 4
17: PCDATA invalid Char value 21
18: PCDATA invalid Char value 31
19: PCDATA invalid Char value 25
20: PCDATA invalid Char value 4
21: StartTag: invalid element name
22: xmlParseEntityRef: no name
23: xmlParseEntityRef: no name
24: Opening and ending tag mismatch: ReferenceList line 3143 and PubDate
25: Opening and ending tag mismatch: PubmedData line 3097 and JournalIssue
26: Opening and ending tag mismatch: PubmedArticle line 2889 and Journal
27: Opening and ending tag mismatch: PubmedArticleSet line 3 and Article
28: Extra content at the end of the document

--- failed re-building ‘easyPM_vignette_html.Rmd’

--- re-building ‘easyPM_vignette_pdf.Rmd’ using rmarkdown
Quitting from lines 39-50 (easyPM_vignette_pdf.Rmd) 
Error: processing vignette 'easyPM_vignette_pdf.Rmd' failed with diagnostics:
1: Input is not proper UTF-8, indicate encoding !
Bytes: 0xF0 0x43 0xFB 0x79
2: Opening and ending tag mismatch: ReferenceList line 746 and Reference
3: Opening and ending tag mismatch: PubmedData line 704 and ReferenceList
4: Opening and ending tag mismatch: PubmedArticle line 443 and PubmedData
5: Opening and ending tag mismatch: PubmedArticleSet line 3 and PubmedArticle
6: Extra content at the end of the document

--- failed re-building ‘easyPM_vignette_pdf.Rmd’

SUMMARY: processing the following files failed:
  ‘easyPM_vignette_html.Rmd’ ‘easyPM_vignette_pdf.Rmd’

Error: Vignette re-building failed.
Error: Duplicate vignette titles.
  Ensure that the %\VignetteIndexEntry lines in the vignette sources
  correspond to the vignette titles.
Execution halted