Question: Is there a difference when the adverbs '*always, continually,forever,etc..*' are used with past simple and past progressive?

For example :

1. He **always/ continually** worked there.
2. He was **always/ continually** working there.

(What is the difference between the above two sentences?)

Answer: 
Sometimes, we use the past continuous as an alternative to the past simple for repeated or routine actions, with a little difference in meaning.

He always/continually worked there.

He was always/continually working there.

The first sentence literally implies that he always worked there, whereas, the second sentence does not literally mean so. It conveys the sense that he appeared to be always working there. In other words, it implies that he was seen to be working there very often.
/simple past/ means **perfect** or done. /always/ can be used in past form when we want to **emphasize** the event.

past progressive follows simple past.
for ex:
*I was reading a novel* when *he knocked the door*.
you could also say:
He knocked the door while I was reading a novel.

as long as I know, adverb of freq /always/ is not good to place in past prog. tense