Why won't the RCA Pearl TH1101A MP3 Player read a mini sd card for external memory? Is it a format issue?

The card you are trying to use is likely a high capacity sd card (SDHC). This player does not support high capacity cards, it only supports microSD cards that are non-high capacity (I think most of them are usually 2GB or less, but you can find them up to 4GB).

The problem was the card was inserted properly. Just a mere incident of stupidity but make sure you here a click from the card and it should read it.

First off, let's talk about the bad news: there are a lot of people who complain about just how picky the Lyra is about which SD cards it can work with. Indeed, the later model Lyra devices on the RCA site itself say "now supports more SD cards" as a feature. Ouch.
Go to a popular memory card vendor like 4AllMemory and you'll find that a search for Lyra-compatible SD cards shows barely a half-dozen matches Lyra-compatible SD Cards
Another issue: Firmware Update 615 you might need to update your firmware to gain better compatibility with various SD cards:targets this specific problem.
While we're listing all the potential problems, it's also worth reporting that there are some reports of Lexar memory cards that require a higher voltage than regular SD cards, meaning that the Lyra either wont start at all, or its battery drains faster than usual.
Comment from the web on this: "Some Lexar memory cards require at least 2.7v to operate. Some Lyra models only use a single AA battery (1.5v). This MAY mean the mp3 player doesn't have enough power to run the card (depends on if RCA used the right parts to temporarily boost the internal voltage to 3v through a booster circuit or capacitors). This may vary between models and even between different releases of the same model. This also may explain why you can hook the device up via usband send/receive files to the card fine but then have problems after you disconnect (a USB wire can provide some amount of power. My previous nexxtech player would actually turn on without a battery when I plugged the usb wire in). "
Generally, you should be hooking your Lyra up to your PC, then running the standard PC disk formatting utility. But even then, here's what RCA warns:
"We have recently discovered an incompatibility with the RD1080/RD1090, windows XP(Service Pack One) and some newer SD cards. We are presently working with microsoftto identify the best approach to correct the issue. Until a solution is implemented, we suggest that you use MMC cards instead of SD. "
To format an external device in Windows XP, just find the device in your "My Computer" window, then right-click on it and choose Format.... You'll see something like this:
(since I don't have a Lyra, this shows the default for my second hard drive. Your settings would be similar, but probably a bit smaller!)
RCA offers zero assistance on the best way to format an SD Card for use with the Lyra, as far as I can tell, so I'll say that my expectation is that NTFS will work, you should use a short, letters-only volume label, and you should not choose either "Quick Format" or to "Enable Compression".
When you're ready, click on Start and it should only take a few seconds for the SD card to be ready to roll with your Lyra.
If it works.

please rank if this helps

Pick internal memory unless you have an SD card attached. Then press the "M" button on the side of the player to see if it will change menus.

-Tha Mp3 Doctor

It will support earlier Sandisk 1GB and 2GB micro SD cards

Stick with an older Sandisk microSD 1GB card - the only one it will reliably read

You probably loaded an incompatible file type - this player is not as resilient when faced with such a possibility
perform a firmware upgrade to
restore it.
– Please go to http://www.rcaaudiovideo.com/faq
for more details.

-Tha Mp3 Doctor

you get from here:
http://www.antonline.com/p_RCA--TH1101--RCA-TH1101-PEARL-SERIES-THUMBDRIVE-MP3-PLAYER-(1-GB)-_312319.htm

Most times the card would have to be formated in the device that is using it.

you should format the Sd card by the software from rio, and I am using 1g SDcard ，I am not sure if 2g sd card works fine.