I had the same problem. You need to remark out the lines 7-11 in the water.ps shader.
Go to ShaderPack\Encryption\Media\Shader (replace ShaderPack with the directory where you extracted the shader files). Open the water.ps file in a text editor. remark lines 7-11
//#ifdef GL_FRAGMENT_PRECISION_HIGH
// precision highp float;
//#else
// precision mediump float;
//#endif
Save the file. The go back up 2 directories to ShaderPack\Encryption and run the Encryption.exe program. Note where the files are saved in the pop-up that appears when the encryption is finished. Navigate to that directory something like C:\users\name\appdata\local\AGKApps\Encryption\media\shader copy the water.pc file from this directory to wherever it appears in the ShaderPack directory.
Also might help to identify what system you are having problems. Might help janbo come up with a more elegant solution.
My specs, HP 15 model f100dx, CPU AMD A8 6410 APU with AMD Radeon R5 graphics. 2.0 GHz, RAM 4 GB, OS WIndows 10 Home