Pretty much the only reason a card would go off after 20 minutes is that it is taking the killer Emm. If thats the case then you need to sort your Tier8's out.
There's loads of info on how to add the proper channel subscription tiers to a card and how to keep dates etc in a reasonable range.
Start by taking all tier8's off the card and then just add one back - try the ones for a basic or mid level package. Dont be tempted to add further channels to this tier and keep the dates sane.
Once you've got that working then slowly add other tiers. Again, dont be tempted to modify channels within any particular tier. Start playing with the channels available within a tier and you stand a good chance of killing your card !
Start simple and build it up !
Hint1: If you have a subbed card then read the tier info with a program like TierInfoLite. This will give you valid tiers and dates which you can then copy onto your Mosc.
Hint2: try not to duplicate entitlements. Its pointless having both a starter package and a supreme package if the supreme package gives you all channels within the starter package !
