Just like the topic says...

When I want to merge mods, alot are not mergeable. I think the error I've gotten each time was that there was a CELL issue.

Why is this? Is it something I can fix? Or are the only mergeable mods simple, texture type of mods?

It is not something that can be fixed. Some types of records are not mergeable, and that includes CELL records. Mergeable mods are green in Wrye Bash.

Edit: http://wryemusings.com/Wrye%20Bash.html#MergePatches

Edit: Just to clarify so that more people do not get confused, this topic is about Bash mergeable plugins, not actually merging multiple plugins.

Thank you. I somewhat understand this now, that t can't be done...not that it's an error or something.

That's what the colors are for... In the future, post Wrye Bash-specific questions in the Wrye Bash thread.