Hello! First time poster, apologies if this is a duplicate... I have read through many similar problems and tried the solutions and they have not worked for me, so I am starting a new post.
I am having trouble installing packages, using R 3.5.2 and R studio 1.1.463.
When I try to download a package I get the error message below. 
This happens for more packages than the tidyverse, I'm just posting one example. I have already tried using a CRAN mirror and unchecking the "use secure download method for HTTP" in tools --> globaloptions --> packages. It seems to be an issue where R can't connect to the repository? I don't know what prompted this as I could download packages just fine until 24 hours ago.
Can anyone help me?
> install.packages("tidyverse")
Warning in install.packages :
unable to access index for repository http://cran.revolutionanalytics.com/src/contrib:
cannot open URL 'http://cran.revolutionanalytics.com/src/contrib/PACKAGES'
Warning in install.packages :
unable to access index for repository http://cran.revolutionanalytics.com/src/contrib:
cannot open URL 'http://cran.revolutionanalytics.com/src/contrib/PACKAGES'
Warning in install.packages :
package ‘tidyverse’ is not available (for R version 3.5.2)
Warning in install.packages :
unable to access index for repository http://cran.revolutionanalytics.com/bin/macosx/el-capitan/contrib/3.5:
cannot open URL 'http://cran.revolutionanalytics.com/bin/macosx/el-capitan/contrib/3.5/PACKAGES'
> chooseCRANmirror()
Secure CRAN mirrors
1: 0-Cloud [https] 2: Australia (Canberra) [https]
3: Australia (Melbourne 1) [https] 4: Australia (Melbourne 2) [https]
5: Australia (Perth) [https] 6: Austria [https]
7: Belgium (Ghent) [https] 8: Brazil (BA) [https]
9: Brazil (PR) [https] 10: Brazil (RJ) [https]
11: Brazil (SP 1) [https] 12: Brazil (SP 2) [https]
13: Bulgaria [https] 14: China (Hong Kong) [https]
15: China (Guangzhou) [https] 16: China (Lanzhou) [https]
17: China (Shanghai) [https] 18: Colombia (Cali) [https]
19: Costa Rica [https] 20: Denmark [https]
21: East Asia [https] 22: Ecuador (Cuenca) [https]
23: Ecuador (Quito) [https] 24: France (Lyon 1) [https]
25: France (Lyon 2) [https] 26: France (Marseille) [https]
27: Germany (Erlangen) [https] 28: Germany (Münster) [https]
29: Germany (Regensburg) [https] 30: Greece [https]
31: Hungary [https] 32: Iceland [https]
33: Indonesia (Jakarta) [https] 34: Italy (Padua) [https]
35: Japan (Tokyo) [https] 36: Korea (Gyeongsan-si) [https]
37: Korea (Seoul 1) [https] 38: Korea (Ulsan) [https]
39: Mexico (Mexico City) [https] 40: Morocco [https]
41: Norway [https] 42: Philippines [https]
43: Russia [https] 44: South Africa (Johannesburg) [https]
45: Spain (A Coruña) [https] 46: Sweden [https]
47: Switzerland [https] 48: Taiwan (Taipei) [https]
49: Turkey (Mersin) [https] 50: UK (Bristol) [https]
51: UK (London 1) [https] 52: USA (IA) [https]
53: USA (KS) [https] 54: USA (MI 1) [https]
55: USA (MI 2) [https] 56: USA (OH) [https]
57: USA (OR) [https] 58: USA (TN) [https]
59: USA (TX 1) [https] 60: Uruguay [https]
61: (other mirrors)
Selection: 53
> install.packages("tidyverse")
Error in install.packages : Updating loaded packages
Restarting R session...
> install.packages("tidyverse")
Warning in install.packages :
unable to access index for repository http://cran.revolutionanalytics.com/src/contrib:
cannot open URL 'http://cran.revolutionanalytics.com/src/contrib/PACKAGES'
Warning in install.packages :
unable to access index for repository http://cran.revolutionanalytics.com/src/contrib:
cannot open URL 'http://cran.revolutionanalytics.com/src/contrib/PACKAGES'
Warning in install.packages :
package ‘tidyverse’ is not available (for R version 3.5.2)
Warning in install.packages :
unable to access index for repository http://cran.revolutionanalytics.com/bin/macosx/el-capitan/contrib/3.5:
cannot open URL 'http://cran.revolutionanalytics.com/bin/macosx/el-capitan/contrib/3.5/PACKAGES'
>