wordpress site down, getting error message when domain includes www

We have a wordpress site, fallsglass.com that FORWARDS to www.sheboyganfallsglass.com.  When you go to WWW.sheboyganfallsglass.com you get an error message which is below.  When you REMOVE the WWW the site displays fine.

Warning: Cannot modify header information - headers already sent by (output started at /home/fallsgla/public_html/wp-blog-header.php:1) in /home/fallsgla/public_html/wp-includes/pluggable.php on line 1178

Called host.  He said it isn't their problem.  The pluggable.php file has not been updated since site went  live on 4/2/15.  Any idea how to fix?  Client is doing A TON of advertising via cable forwarding people to his site and is sweating bullets with site down.
nsitedesignsAsked:
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Jason C. LevineDon't talk to me.Commented:
How are you forwarding the fallsglass.com site?
Jason C. LevineDon't talk to me.Commented:
Pretty sure this is one of two things:

1) There is a bad plugin or plugin setting. Pluggable.php is the WordPress plugin system and it won't be modified by anything.  But a bad plugin config or setting can cause it to throw an error.

Disable all plugins.  Does the problem still happen?

2) The A records on sheboyganfallsglass.com are not set correctly so www.domain.com is not mapping to domain.com and for whatever reason it's dying right at pluggable.

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nsitedesignsAuthor Commented:
They are using a C name instead of A record. This is kinda of out of my league.  He added the following:

www.fallsglass.com forward to ip address
sheboyganfallsglass.com forwards to ip address
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nsitedesignsAuthor Commented:
p.s. some plugins have been updated.  should I go in and update them in wordpress?  maybe that will fix issue.
Jason C. LevineDon't talk to me.Commented:
A records work better for this than CNAMES.  If you are not comfortable or experienced with making these sorts of changes, I do suggest re-contacting the ISP and asking them to review the DNS (which should be their issue) to make sure sheboygan is set to forward using www and non-www urls.

How about disabling all plugins?  Does that have any affect?
Jason C. LevineDon't talk to me.Commented:
p.s. some plugins have been updated.  should I go in and update them in wordpress?  maybe that will fix issue.

Unlikely, but sure...try it.

If it doesn't work, disable everything to rule out plugins as the issue.
nsitedesignsAuthor Commented:
Thanks for quick response.  I will check with host to see if A record is set properly.  If it is, I will try modifying the plugins.  I did see that some of the plugins need updating.
nsitedesignsAuthor Commented:
I disabled all plugins.  No effect.  I updated plugins.  Site did give me a new error message.  I clicked refresh and now it appears to be working fine again.  Not sure what the problem was.

p.s.  Host changed from C Name to A Record.  Perhaps that helped fix issue?
Jason C. LevineDon't talk to me.Commented:
p.s.  Host changed from C Name to A Record.  Perhaps that helped fix issue?

Likely.  My guess is a combination of issues caused by the CNAME making a funky request.  Fix that, update plugins, and the house of cards stabilized.
nsitedesignsAuthor Commented:
Very glad it did too!
nsitedesignsAuthor Commented:
Site went down again today with same error message.

Warning: Cannot modify header information - headers already sent by (output started at /home/fallsgla/public_html/wp-blog-header.php:1) in /home/fallsgla/public_html/wp-includes/pluggable.php on line 1178

I disabled all plugins and slowly enabled the ones that are vital for site to function.  Why would it work fine for months, then on Oct 1, site goes down, we fix, works fine and now today site is down again with same message?
Jason C. LevineDon't talk to me.Commented:
Is something happening on a monthly or weekly rotation (e.g. Log file rotation) that would cause a memory problem?
nsitedesignsAuthor Commented:
Left message with host to let me know if he can check out file log to see which files were updated since Oct 1.  I will also ask him about log file rotation. Thanks!
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