Stormonu
NeoGrognard
TSR converted the first edition Dragonlance modules (DL series) to second edition (DLC series). This should have been a easy job; one conversion instead of many, between two very close systems.
They failed, from what I've read. DL1 ended in a challenging encounter with an ancient black dragon. The corresponding 2e module ended in a fight with an ancient black dragon--but now, since 2e powered up dragons significantly, the same ancient black dragon would wipe out a party of level 4-6. Do the same sort of naive conversion to 3.5, and you'll end that adventure with a CR 19 encounter.
This does bring up a point; Dragonlance is perhaps the only module series I know of that has had a conversion for each of the major editions, with the exception of 4E. It started as 1E, has a version (as mentioned above) for 2E and SAGA, and likewise has a version for 3.5. While it does span some 15 modules, the amount of rewrite to balance it for each edition is extensive. It's not just replacing a stat block here or there; in some cases the entire encounter has been heavily rewritten - as prosfileas mentioned above.
As a side note, for my last campaign 2-3 years ago, I did a conversion of the 1E C1 - Shrine of Tamoachan to 3.5E. I don't remember how long it took to convert, but it sure felt like more than 8 hours. Plus, the issue of the poison gas filling the lower levels almost made it impossible in play to feasibly complete, with 3.5E's assumed "4 encounters per day". Once again, a seemingly innocuous detail turned out to be a bear in actual play.