SSMS 2008 R2 no longer connects to database

Before Christmas I had no problem connecting SSMS 2008 R2 to a specific remote database. Since Christmas, I get this error when I try to connect:

TITLE: Connect to Server

Cannot connect to [IP ADDRESS].

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ADDITIONAL INFORMATION:

An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)

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A transport-level error has occurred when receiving results from the server. (provider: TCP Provider, error: 0 - The semaphore timeout period has expired.) (Microsoft SQL Server, Error: 121)

For help, click: http://ift.tt/1ColNFm

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Any idea why this is happening? The link provided in the error message gives no information at all.

As far as I know, no updates or changes have been made to SSMS 2008 R2 or the database since the happy time when I could connect and now.

Any help much appreciated.