You have probably uploaded some huge product image. Thirtybees is trying to generate image thumbnail, but because of the source image size it take too kuch time, and pho script time out.
You can either increase script running time (in your cpanel look for max_execution_time settings). If that is not possible, then delete the file you have uploaded.
To do that, you first need to know image ID. This can be deducted from exception stacktrace, look for function parameter value, there will be some id_image somewhere). Once you know the ID, for example 1234, then delete file /img/p/1/2/3/4/1234.jpg