FAILED FOR AN UNDETERMINED REASON. TYPICALLY THIS PROBLEM OCCURS DUE TO CERTIFICATES THAT THE BROWSER DOES NOT TRUST. IF YOU ARE USING SELF-SIGNED OR CUSTOM CERTIFICATES, OPEN THE URL BELOW IN A NEW BROWSER TAB AND ACCEPT THE CERTIFICATE, THEN RETRY THE OPERATION”
UNABLE TO UPLOAD FILE IN DATASTORE “THE OPERATION FAILED FOR AN UNDETERMINED REASON.
Whenever we are trying to upload the files in VMware ESXi Datastore its getting failed with bellow error
UNABLE TO UPLOAD FILE IN DATASTORE “THE OPERATION FAILED FOR AN UNDETERMINED REASON. TYPICALLY, THIS PROBLEM OCCURS DUE TO CERTIFICATES THAT THE BROWSER DOES NOT TRUST. IF YOU ARE USING SELF-SIGNED OR CUSTOM CERTIFICATES, OPEN THE URL BELOW IN A NEW BROWSER TAB AND ACCEPT THE CERTIFICATE, THEN RETRY THE OPERATION”
Solution 1
How to download and import CA certificate in windows machine for browses trusted certificate.
VMware vCenter 6.0,6.5,7,ESXi-6.0,6.5,7.
First Download the trusted root Certificate by entering Hostname or IP address of VMware vCenter in browser.

Save the download file in location and extract it using windows explorer or any software

Open run with win+ R and type certmgr.msc

Goto -> All Tasks :- Import

Select the certificate from the directory and click Next

Click on place all certificate in the following store

Click on Finish

Click Yes to add the thumbprint(sh1)

We can see the certificate imported successfully.

Restart the browsers and Enter the hostname or IP
We can see that no certificate issue

Now You can upload the file successfully.
If the problem is not solved you can refer below
Solution 2 :-
- Take SSH or putty of vCenter Server appliance for 6.0
Type “Shell” to enter in shell prompt
root# service vsphere-client stop
root# rm -rf /etc/vmware-vsphere-client/SerenityDB/serenity/*
root# service vsphere-client start
2.For VMware vSphere 6.5.x,6.7.x & 7.0.0 follow the below path
root# service-control --stop vsphere-client
root# rm -rf /storage/vsphere-client/SerenityDB/serenity/*
root# service-control --start vsphere-client
3. For Windows installed VMware vCenter Server.
⇒C:\Users\MasteringNutanix>cd <C:\Program Files\VMware\vCenter Server\bin>
⇒vCenter Server\bin> service-control –stop vspherewebclientsvc
4. Delete the contents of the below folder.
⇒C:\programdata\vmware\vCenterServer\data\vSphere Web Client\SerenityDB\serenity>
⇒serenity> service-control –start vspherewebclientsvc
Reference :-