I don't think there's a limit but could be wrong. FileMaker 12 supports up to 9 other guests that can connect to the hosted file.
You might check this issue to see if it is a factor:
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: https://www.dropbox.com/s/jt09b82i0xijbu3/FMP%20Bugs.zip
Thank you for posting this! I think this may be the issue as I can't see the .pem files in the FMP12 folder. Unfortunately I don't have admin rights so I can't copy them across from 7 to test this out, but I will log a call and post back and let you know if it works.
Thanks for your help and getting back to me so quickly!
Unfortunately this fix has not worked. Our administrator copied the server.pem file from our exisiting versions of FMP7 into the FMP12 folders and we restarted our PCs but still can't access files remotely.
Could it be because the version we got the .pem file from is too old? I saw that someone else has been having a similar problem (http://forums.filemaker.com/posts/61c8fa45bf) and had fixed it by installing the file downloaded from http://www.yazalim.com/filemaker-networking-file/ - is there any chance that this would work, even though the other one didn't?
Our network administrator thinks that the server.pem file may have been excluded from the trial package on purpose, and that it would be there if we went ahead and bought the full version. But it seems very unlikely to me that they would release a trial where you can't use one of the key features!
12 was a major upgrade. 12 can't run fp7 files as is, it must convert to fmp12. I would say the older pem are not compatible. As far as I know Filemaker trail is the same as the full version, except it has a 30 day limit. I don't think purchasing the full version will fix your problem. Filemaker has free installation support on purchased versions of the filemaker. You may have to completely remove filemaker and then reinstall.
Just a couple of additonal note: Older versions of filemaker can not read fmp12. FMP12 has to convert the database to FMP12 format, which FMP12 makes a copy of the databases and converts. Just to clarify, incase you didn't know.
I would simply call FileMaker and ask them. If it's the main reason for upgrading, I'm sure they will want to help you.
Thanks S Chamblee and Steve! I really appreciate those suggestions and clarifications. As you may have guessed I'm not technical myself and our IT support are not that knowledgeable about filemaker so this is really helpful. Thank you!