I am happy to buy a replacement sim, I am just curious to know if anyone knows why one sim would be accepted and not another connected sim:

I recently bought a Huawei E353 dongle from overseas, unlocked but with a foreign operators dashboard on it (yeah, I know that's asking for trouble). I installed the generic Huawei dashboard, and it mostly works with no problems.

This dongle refuses to register on the network with my 2DM prepaid sim, but works 100% with my 2DM post pay sim, and also OK with a Telecom prepay sim.

I have checked the rejected sim in 2 other dongles, nokia and android phones and it works fine in all.

I have tried manual and auto network selection. It sees the 2DM 2G and 3G but won't register on either. Signal strength is strong in my area.

The prepaid sim and post paid sim have very similar serial numbers on them - the last 5 digits are different. They physically have the same printing/branding on them. The post pay sim is quite old, the prepaid sim is probably a year to 2 younger.

Just to clarify, this is not an APN issue, it isn't getting that far - it fails to register on the 2DM network at all with the rejected sim.