Try the .net repair tool
Log on a Windows session with a local administrator account.
A) Uninstall all .Net FrameWorks (from 1 to latest in reverse order) from Programs and Features > Uninstall. Try uninstalling .Net from latest version to older version.
Go to Control Panel > Programs and Features > click 'Turn Windows features on or off' > uncheck 'Microsoft .Net Framework 3.5.1' and 'Microsoft .Net Framework 4.6'> ok
Download .net cleanup utility (dotnetfx_cleanup_tool.zip) from following site:
Unzip it >Run cleanup_tool.exe >In dialog Products to cleanup: .net Frameworks – All versions >select ‘Cleanup Now’.
C) Restart computer
E) Go to Control Panel > Programs and Features > click 'Turn Windows features on or off' > check 'Microsoft .Net Framework 3.5.1' and 'Microsoft .Net Framework 4.6'> ok
E) Restart computer and reconfirm behavior.
There is also a command than compiles all pending .net assemblies. It's something like this "c:\Windows\Microsoft.NET\Framework\v2.0.50727\ngen executeQueuedItems"
I believe you need to do this for all installed .net versions.
If that doesn't work your probably best of reinstalling the OS. Finding the cause of .net errors might cost more time.
What version are you using? In 2016 or 2015 whenever they integrated PDM profession with the install I was having DLL errors when I tried to load PDM on a contributor machine, not even my VAR figured it out. But once I installed the full version of solidworks it registered the DLLs and I was able to use PDM.
I will say I have installed PDM 2018sp1 for a contributor today without installing Solidworks and it worked just fine
Other option, register the DLL yourself
Locate the DLL
Open the Run command (Windows R)
type in "regsvr32" (Without quotations)
drag and drop the DLL into the run command next to the regsvr32