Welcome once again to the Forum
I've seen this happen before. Likely scenario is that the person you bought the laptop from did a classic hack known as the "no-1802" utility. The purpose of the "no-1802" utility is to flip a single bit in the BIOS settings to disable the wireless card "whitelist" checklist of acceptable cards. These laptops have a list of certain cards they will accept. It's likely your laptop originally had a "wireless B" card such as the Intel WM3B2100 and the person you bought it from wanted to upgrade to a "wireless G" card such as the Intel WM3B2200BG, which is newer and faster. So they removed the old wireless "B" card, ran the "no-1802" utility to remove wireless card limitations, and then installed a wireless "G" card.
However, the "no-1802" utility program is dependent on a working CMOS battery. (Besides the main battery, your laptop uses a small, nickel-size CMOS watch battery to keep date/time and other basic settings). The problem is that when the CMOS battery dies (they have a lifespan of about 3-5 years or maybe more), the "no-1802" settings allowing the newer wireless card to work will be lost, and the infamous "1802: Unauthorized network card is plugged in. Power off and remove the miniPCI network card
" error will return.
More info. about the no-1802 error fix here: http://www.command-tab.com/2006/02/26/t ... error-fix/
and here: http://www.thinkwiki.org/wiki/Problem_w ... twork_card
There is a lot of technical information there, but I post these references for the benefit of others who may be reading this thread.
In your case the solution will be very simple. Firstly, you must supply us with the 7-digit type/model number of your Thinkpad as Ray mentions above. Secondly, you will have to open up the laptop and remove the mini-PCI wireless card. (Don't worry, it's not that hard to do. And with these older laptops the wireless card is sometimes located in a slot on the back of the laptop, which will be easier than having to remove the keyboard). Thirdly, (assuming the CMOS battery is dead or dying), you will need to replace the CMOS battery. Finally, (assuming the wireless card is good), you will download and run the "no-1802" utility and then then re-install the same card. If the card has gone bad, then you will need to replace the card. They are not that expensive.
The annoying thing about this error is that it will not allow you to boot or press "ESC" or get past the "1802" error and use your laptop until you remove the card. I am not sure if you can get into BIOS settings using "F1" at startup, disable the wireless card in BIOS settings, and at least use your laptop in the mean time. I've never tried that.
Do you access the Internet by plugging a network cable into the side or by using the internal wireless card of the laptop? If you plug in a network cable then you can simply remove the wireless card and just plug in your network cable for Internet access. If you want to access the Internet wirelessly, you will need to follow the steps outlined above to fix this error.
Read this thread about someone who had a similar issue: viewtopic.php?f=45&t=96766
Unfortunately, the person we tried to help in that thread never responded back, so we don't know if changing the CMOS battery and running the "no-1802" utility resolved the problem.
It will be nice for us to to find a solid solution to this problem so I hope you will report back to us. This will help many others who may encounter this error.