Random syntax errors in script

I have a very puzzling problem in Python 2.7 I use Notepadd++ After developing a script of no more than 25 lines, when running it on Python it gives me "Syntax Errors" on different lines of the script on re-running it even if the that line runs OK on the interpreter. For instance, on simple statements like assigning a value to a variable, the second or third assignment to that variable gives me the syntax error. I went to the length of typing line by line on the interpreter and each executed with success, arriving at the proper result in the last line. I tried to re-write and run the same script (copying line by line) on IDLE (which gives me also random line syntax errors) and lastly resorting to Microsoft Notepad. No better. Please your help will make me understand such a complex language as Python. Thank you. I use WIndows 10 and the script is a test of Hashing and AES encrypting from Crypto.Hash / Crypto.cipher. I am ready to furnish a copy of the script.