I had begun using TrueCrypt to encrypt some data partitions. It had a few advantages over Bitlocker, which appeared to be the main free alternative; for example, Bitlocker was available only in the Ultimate and Enterprise versions of Windows 7. Using TrueCrypt had been slightly awkward at first, but by this point I had gotten used to it.
But now there was a problem. I had several encounters with a TrueCrypt error message: “Incorrect password or not a TrueCrypt volume.” I had gotten this message only with drives connected to the computer via USB. In other words, as of this writing, it appeared that an immediate precaution, to avoid further encounters with the error, would be to use TrueCrypt with drives mounted internally. I had experienced the error with a Western Digital (WD) Passport drive, which is powered only via the USB connection itself, and I had also experienced it with two or three different internal hard drives mounted in external drive bays connected via USB.
A search led to various possibilities. I felt a virus was unlikely, as I was not having these problems with TrueCrypt volumes installed inside laptop or desktop computers. One thread discussed issues with special characters in passwords. A TrueCrypt page suggested trying to restore the volume header from the backup embedded in the volume. Pursuing that option exposed me to the possibility that I could perhaps save the volume header in a separate file. I was not sure whether doing so would adversely affect security. One user suspected a possible adverse interaction from using a disk maintenance tool (in that case, Hiren’s Boot CD) while the TrueCrypt drive was connected. A long thread discussed other possibilities.
These suggestions did not work for me. But they did alert me to two possible explanations in my case. One was that I had gotten the “Incorrect password” error only when I had two or more external USB drives connected to the same computer. At first, I had thought the culprit was a USB hub that I was using to connect multiple devices to the laptop. But I ruled that out (or at least I stopped thinking that was the core problem) when I had the same problem, on two different occasions, with two hard drives connected directly via USB to the desktop machine. Anyway, I had often had multiple external USB drives connected to the desktop machine simultaneously, and had not previously experienced this.
That led me to another possibility. I had recently moved. In my new location, I now realized, I had plugged the external USB drives into a power strip plugged directly into the wall outlet. Previously, as I recalled, I had powered my external USB drive bays by plugging them into a power strip plugged into my battery backup. In other words, I wondered whether fluctuations in the current supplied by my local electrical utility was upsetting the USB drives. This could be an explanation for the failure of the WD Passport as well, because its problem had occurred when I had it connected to that external USB hub, which was likewise plugged into the power strip connected directly to the wall outlet.
I replugged the external drives so that their AC power came through the battery backup. It would take an overnight, possibly a shutdown and restart, possibly a few days, but I would soon see whether this change resolved the issue. Even if it did, I had to realize that this problem could recur whenever a battery backup was not available — although the electrical utility in this particular locale seemed to be in the spotlight, as I had not experienced the error while using a more expensive external drive enclosure in multiple locations during an extended camping trip.
Ten days after moving the plugs (i.e., powering the USB drives and hub through the battery backup), I had no further recurrences of the TrueCrypt problem. During these days, the drives and hub were connected, first, to the desktop, and then, later, to a laptop. Then I had some days when I had to do without the battery backup. During those days, the USB drives and hub were connected only to the laptop and, once again, were powered directly from the wall outlet — or, more specifically, through a power strip plugged into the wall outlet. This was, I think, not the same power strip that I had used with them previously. The TrueCrypt error still did not recur. I was not sure what this meant. It could be that the battery backup was essential and I was just lucky during this time; it could have meant that the local electric utility had just hit a temporary rough patch, when I got those TrueCrypt errors; it could possibly have pointed toward a problem in the power strip’s surge protection circuitry (or to some compounded problem arising from the fact that, to further clarify, I actually had one power strip plugged into another).