"When we worked together" vs "when we were working together" or can I use "when" with continous tenses?

In one Russian discussion group devoted to ESL, I was advised that using when with continuous tenses is incorrect in English.

To be exact, we were discussing how to translate a phrase about one’s former collegue. So two possible translations were:

1. When we worked together she was (used to be) nice.
2. When we were working together she was nice (to me).

I do agree that using simple tenses might be a better choice here. The question is whether the use of continuous tenses is always a mistake — is it?

I think the important thing to keep in mind for a non-native speaker of English is that when the reference time is in the past, there are two ways to render a habitual meaning: with a simple preterite form, and with the compound past continuous form. So in general, both of the forms should be correct.

This is true, however, only for verbs whose meanings involve an action which has a palpable duration like work, live. e.g.,

1. When I lived in Utrecht, I used to love to take walks.
2. When I was living in Utrecht, I used to love to take walks.

For verbs with punctual meaning, like fall, only the simple preterite form is appropriate for a habitual meaning, and whenever is more appropriate than when. e.g.,

1. Whenever I fell, Thomas would help me up. (refers to a habitual event)
2. ?When I was falling, Thomas helped me up. (sounds odd, because it would refer to a single act of falling)

The second sentence might sound odd because "while" not "when" is more commonly used in conjunction with the past continuous. "While" has the sense of "for a non-specific duration of time." This pairs well with the past continuous to describe an event that happened during a prolonged, non-specific time in the not-too-distant past. "When" on the other hand has the sense of "a specific time", and as such works well with the past simple.

However, in your example, there is no discernible difference because the time frame itself is non-specific to the reader. We don't know how long you worked together. As well, being nice is an action that is hard to quantify in time. Because of that, the past simple or the past continuous can describe that period of time equally well. Moreover, "when" with the past continuous has a good argument in its favor, in that we commonly use "when" with the PC when referring to "ages or periods of time in the past". An example of this would be "When I was in college, Adidas sweatpants were the fashion." Time in college is a specific period of life. Compare that to "While I was walking the dog, I remembered my mom's birthday." Walking the dog here is a non-specific time frame, and so while would be expected. In the case of your example, your employment with the woman who was nice to you could be represented as a "period of time."

Per the BBC: We also use when, not while, to talk about periods of time in the past.

In a completely different direction, the one criticism that is often levied against the past continuous is that, when used unnecessarily, it sounds long-winded.