the error messages explain it completely.
TimeGMT() is a predefined function of mql4 and your FFcal.mq4 contains a individual function with the same name.
This naming collision is the reason for these error messages.
Just replace every TimeGMT phrase in your code with a different name like FFTimeGMT and it will compile without any error.
But here is a new error message:
I get the following error trying to attach the
FFcal.mq4 to my MT4 platform (and the error appears in a dialog box
FFCal Error - Web page download was not complete!
All these things were discussed before.
Check this thread: https://www.mql5.com/en/forum/149321
Or use the forum search to get more information