[ error ] ofShader: begin(): couldn't begin, shader not loaded

Trying to merge 2 different projects and now getting a runtime error

[ error ] ofShader: begin(): couldn’t begin, shader not loaded"

Can anyone suggest most likely causes for this error?

most probably you forgot to load the shader at all, the name of the shader file is not correct or it failed compiling. take a look at the rest of the output to see if there’s any more details about the error