An error occurred while signing: SignTool.exe not found

Please Click Once application --> Properties --> Signing -> Unchecked the Sign the ClickOnce manifests.

Problem will be solved.

Note: Be aware that this solution removes security from your project. Seek assitance from a more learned colleague before doing so.

You can fix this by clicking on installation application of VS. Then click Modify > Mark ClickOnce App and then upgrade your VS. Also i think @Alex Erygin is right. It is a bad solution to Click Once application --> Properties --> Signing -> Uncheck Sign the ClickOnce manifests. This is not a solution. It only circumambulated the problem.

ClickOnce Publishing Tools are not installed as part of the Typical Installation Options. So you have to install it in advanced mode.

This dialog can be found in Windows 7 by going to Control Panel > Uninstall a program, right-clicking on Microsoft Visual Studio Professional 2015 and selecting Change. A Visual Studio dialog will open up. Select Modify from the set of buttons at the bottom and the above dialog will appear.

SignTool is moved to another location in the last SDK: C:\Program Files (x86)\Windows Kits\8.1\bin\x86

Need to install ClickOnce Publishing Tools during Visual Studio 2015 setup.

You can re-run the Installation from the Programs and Features section; find Visual Studio in the list and click Change.