As mentioned here the watermark file can cause an issue accessing Sage line 50 but the problem can be two fold. The version of the Sage client can be subtly different between the highest patch revision and the lowest. In this case I tracked down that depending on the order of which client accessed the sage data and the creation of the watermark.xml file – the final client could not access until the watermark file was removed. Checking the contents lead me to double check that the Sage clients where all the same version (right down to the patches they had) and lo – the one with the problem did not have the exact version.
A quick check showed that a missing update (update 2 for Sage 2010) was required. Installed this as admin and was able to start and access the data as this client machine without error. It appears its a bug in the Sage client that it does not notice the missing patch when it checks for updates.
So the moral here is – if you get the message re the data being accessing via a later version of sage. Check the watermark file contents and the use help about on the clients to identify any differences. Speak to Sage if you have a support contract and make sure all the patches are applied.