What EXACTLY does the error message say? If it says you can buy items requiring immediate payment, That error message seems to be associated with running into your Open Transaction Limits. To get below your limits you need to pay for the outstanding unpaid items that now count towards your limits, but that might not be immediately possible because eBay counts items that you committed to buy but cannot pay for at this time against your limits:
1. At least some active auctions that you have bid on (including the one you are trying to rebid on). Originally only those you were in the lead on counted, but it is very likely that the rules have changed since they were last made public to include your outbid bids on running auctions and also any pending Best Offer. To minimize the effect of these wait until near the end of the auction to bid only one time at your TRUE maximum you are willing to pay for the item, and then pay immediately after it ends, to minimize the time it counts towards your limit. You can't pay until you win, so don't use up your open transactions on bids you can't pay for until hours or days later. Waiting to bid also keeps your options open (once you bid you are committed to that auction and can win and have to pay even if you are outbid during the auction--exception if it is still "Reserve not met" after you bid) so you can safely bid on an auction that ends earlier or jump on a great Buy It Now price that gets listed in the interim.
2. Transactions cancelled at your request (or due to problems with your address). Note that these also can result in lowering the limit, so make sure you are going to buy (and CAN buy, that the item ships to your location) BEFORE you commit to buying.
3. Unpaid Item Strikes. Again, don't bid/commit to buy unless you KNOW you can and will pay for every item.
To get these and other buying limits raised or removed in the long run you need to establish a pattern of reliably paying for what you commit to buy.
