MultiBit has long been abandoned. Multibit Classic was extremely unreliable for me and it didn't work for a long time.

You have to export your keys to somewhere else. To do that, you can either try to send the coins to another address or to export it altogether.
To try to fix this, go to Tools>Reset Blockchain and transactions and select the option to reset. Send the coins to a newly created Electrum wallet with the seed.

If the above doesn't work, go to Tools>Export Private Keys. Select your directory to export it to and don't encrypt it with a password. Next, open the file (.key) with any word editor like NotePad. Copy the string of letters beside your address that you wish to export. Go to your Electrum wallet and go to Wallet>Private Keys>Sweep and paste it inside the box. Press sweep and the coins will be on their way to your Electrum address. Remember to backup the seed.