Apart from all teh stuff listed above there is no reason. Defective strings are a rarity too.
Wiht the higher strings (E & A) tune very gently sudden changes in tension can be counter productive. More expensive strings don't usually need too much stretching in. If you're worried then tune it a semi tone low and play it like that for a while - it will sound strange but what the hell!
What are you using to tune it with - chromatic Electronic - is it set to C? I accidentally set mine to A once and nearly did damage.
The best bet is talk to another fiddler. Where are you there are probably some of us near you might be able to help out or know someone who can.
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sj