iMac os x 10.6.8 will not connect to a specific server

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I am having a problem connecting to a specific server on my imac running 10.6.8. This mac has connected to this server before, and I can connect to other servers on this mac. I can connect to the specific server on my other imac, but I can't figure out why the one running 10.6.8 will not connect. I have tried connecting by smb:// and typing the ip address and also tried the server name. It was connecting fine last week but now it will not. It is a Windows server, could it be a security issue on the server? I know this is an old system, so I tried updating to 10.7.5 and still get the same error connecting to the server. Check the server name or IP address. Any ideas? I can also ping the server through the terminal app.