First time I tried the blockchain app "for real", ie, not testing with 0.01BTC test transactions, it failed rather miserably
I wanted to sell 50BTC to a friend. I brought my android phone, tried sending him 50BTC from my blockchain wallet, and it told me the wallet didnt support more than 16kb.. of.. ? inputs? not sure. So I tried 25BTC, same error. Tried 5BTC, and that worked, but took forever.
So I switched to my laptop, went to the blockchain site and did the same in the browser, and the result was the same. 10BTC transactions worked, but took forever, and 20+BTC transactions failed due to that 16Kb limit.
What happened is you've been receiving a large number of small payments. Each payment to you is a separate transaction. When bitcoin wants to spend the value of a transaction each separate transaction has to be included as an "input" to the new transaction you make. Each input takes up some space, and unfortunately you had enough transactions to exceed blockchain.info's *size* limit. This isn't actually a limit on how *much* BTC you're trying to send, but rather, the form it took when it was sent to you. For instance, if I sent you 50BTC in one payment you would have a transaction that looked like this:
TX#1: retep says P4man can have 50BTC, using the outputs of transactions...
Now to spend it, you would create a new transaction:
TX#2: P4man says someguy can have 50BTC, using the output of transaction TX#1
In your case though, you have a few dozen transactions, so when you try to spend it, the new transaction looks like this:
TX#2: P4man says someguy can have 50BTC, using the output of transaction TX#1, TX#2, #3, #4 and so on.
http://blockchain.info/tx-index/4947507/d17258cfb9970b8715e5ed7e62822b08aaccd6368dc563666758f59de6f300e2 <- here's a good example of a transaction that needed a lot of inputs. It looks kinda funny having the same "from" address multiple times, but it actually just means that multiple small transaction *to* the address 18oh1W4a3WpybAW8CCnBqSVgKBdjgQULr2 were made, and the new transaction needed multiple inputs to spend them all. The reason why it took so long to create those transactions BTW is just that blockchain.info uses a relatively slow javascript implementation of the cryptography used in bitcoin.
As a practical point of view, next time you find you're getting a lot of transactions, it can help if you create a payment to *yourself*. Your wallet software will bundle up a bunch of transactions into a single one, and then the next time you need to spend it you only have to include the output of that one transaction.
Out of curiosity... have you been playing satoshidice?