Hello
Thank you for your question and reaching out. I can understand you are having query\issues related to .net framework install on Windows server.
- Disable any Antivirus program or Windows firewall you may have for temporary purpose.
- Run sfc /scannow from elevated prompt.
- Please mount original iso using which you have installed Windows server, then run below command to install it.
dism /online /enable-feature /featurename:NetFX3 /all /Source:d:sourcessxs /LimitAccess
Note : Change the source to the ISO/Media
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