Spanish term (edited): funcion� bien en sus inicios

That's how I'd say it.

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Note added at 3 hrs 38 mins (2004-07-01 20:49:17 GMT)
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Thanks to everyone who has shown their support to this answer. I believe the tricky parts here are the preposition and the tense. If one were to use \"since\" or \"from\" it would mean it\'s still working (and we don\'t know that from what little information we have), \"at\" and \"was\" both imply that it no longer works well, which we also don\'t know.

I used \"in\" because it covers both possibilities (it worked well in the beginning but it no longer works, it worked well in the beginning and it still does - hence the \"credibility\" part that follows...).

So the asker should choose based on the rest of the information, and I\'m sure she\'ll let us know ;).