It's because you sent too large amount to include in block in its current size. In case you received your karbo in small portions (e.g. 1-2 krb at time) when you're trying to send them at once the amount of inputs is large and transaction is too big in bytes, larger than current median block size. When transaction count and amounts increase in future median may increase.
Unconfirmed transaction sits in transactions pool for 24 hours and then is deleted and funds are released back to wallet.
What should you do now is to wait 24 hours until your funds return to your wallet and then send them in smaller chunks (say 100 krb at once in case you got them in 1-2 per transaction, or 500 krb if you got 20-30 krb per transaction). You can also reset wallet when funds are back just in case to ensure you don't have some wrong amounts, and if you don't want to see that unconfirmed transaction. To reset wallet use menu File -> Reset wallet in GUI and type 'reset' in simplewallet CLI.
If you need to sen larger sum at one you can send smaller sums to yourself thus consolidating your inputs and transaction will be smaller.
For example, this is large transaction consolidating 2000 krb, where there is a lot of small inputs (212) that is quite a lot, and only 13 outputs, the size of transaction is 22989:
http://democats.org/blockchain/transaction/?name=karbowanec&hash=9991BEBC01FFC8A86A49919CEA6E4889770BEF17B4A4198592454EDC094BB3BACompare with sending 10000 krb constisting of such optimized inputs (3), it's only 724 bytes:
http://democats.org/blockchain/transaction/?name=karbowanec&hash=610264FB1B14F453AB3D401E3DE7B833C680D059001BF4D1C777729C5D0467C7 
I cant withdraw my coins from Cryptopia:
That is bullshitcoin!
