I keep getting below error when opening the frame. I have tried disabling all addons, but this didn't help.
Using 10.1.5.1 on retail

12x MerchantPlus/MerchantPlus.lua:243: attempt to index global 'MerchantFrameBottomRightBorder' (a nil value)
[string "@MerchantPlus/MerchantPlus.lua"]:243: in function UpdateFrame' [string "@MerchantPlus/MerchantPlus.lua"]:180: in function <MerchantPlus/MerchantPlus.lua:135> [string "=[C]"]: in function PanelTemplates_SetTab'
[string "@MerchantPlus/MerchantPlus.lua"]:147: in function <MerchantPlus/MerchantPlus.lua:135>
[string "=[C]"]: in function PanelTemplates_SetTab' [string "@FrameXML/MerchantFrame.lua"]:100: in function <FrameXML/MerchantFrame.lua:93> [string "=[C]"]: in function Show'
[string "@FrameXML/UIParent.lua"]:2936: in function SetUIPanel' [string "@FrameXML/UIParent.lua"]:2836: in function ShowUIPanel'
[string "@FrameXML/UIParent.lua"]:2644: in function <FrameXML/UIParent.lua:2640>
[string "=[C]"]: in function SetAttribute' [string "@FrameXML/UIParent.lua"]:3246: in function ShowUIPanel'
[string "@FrameXML/MerchantFrame.lua"]:27: in function showFunc' [string "@FrameXML/PlayerInteractionFrameManager.lua"]:183: in function ShowFrame'
[string "@FrameXML/PlayerInteractionFrameManager.lua"]:215: in function <FrameXML/PlayerInteractionFrameManager.lua:212>

Locals:
self =

{
GetOption = defined @MerchantPlus/MerchantPlus.lua:68
GetAceOption = defined @MerchantPlus/MerchantPlus.lua:78
Init = defined @MerchantPlus/MerchantPlus.lua:446
UpdateFrame = defined @MerchantPlus/MerchantPlus.lua:187
UpdateSort = defined @MerchantPlus/MerchantPlus.lua:327
ClearMerchantTaint = defined @MerchantPlus/MerchantPlus.lua:438
ClearTaint = defined @MerchantPlus/MerchantPlus.lua:424
HandleEvent = defined @MerchantPlus/MerchantPlus.lua:346
UpdateBuyback = defined @MerchantPlus/MerchantPlus.lua:270
Events = Frame {
}
UpdateColumns = defined @MerchantPlus/MerchantPlus.lua:322
SetTableLayout = defined @MerchantPlus/MerchantPlus.lua:304
HandleBuyback = defined @MerchantPlus/MerchantPlus.lua:252
SetAceOption = defined @MerchantPlus/MerchantPlus.lua:102
SetTab = defined @MerchantPlus/MerchantPlus.lua:135
}
show = true
buyback = false
width = 800
(*temporary) = nil
(*temporary) = nil
(*temporary) =
(*temporary) = "BOTTOMRIGHT"
(*temporary) = MerchantFrame {
0 =
SetPortraitShown = defined @SharedXML/PortraitFrame.lua:102
GetTitleText = defined @SharedXML/PortraitFrame.lua:28
SetPortraitTexCoord = defined @SharedXML/PortraitFrame.lua:98
SetPortraitTextureRaw = defined @SharedXML/PortraitFrame.lua:84
SetPortraitToClassIcon = defined @SharedXML/PortraitFrame.lua:92
lastTab = 1
TitleContainer = Frame {
}
SetTitleMaxLinesAndHeight = defined @SharedXML/PortraitFrame.lua:49
SetTitleColor = defined @SharedXML/PortraitFrame.lua:32
Tabs = {
}
SetTitle = defined @SharedXML/PortraitFrame.lua:36
lootFilter = MerchantFrameLootFilter {
}
SetTitleOffsets = defined @SharedXML/PortraitFrame.lua:54
SetBorder = defined @SharedXML/PortraitFrame.lua:67
layoutType = "PortraitFrameTemplate"
SetFrameLevelsFromBaseLevel = defined @SharedXML/PortraitFrame.lua:120
SetPortraitToBag = defined @SharedXML/PortraitFrame.lua:80
PortraitContainer = Frame {
}
SetPortraitToUnit = defined @SharedXML/PortraitFrame.lua:76
Bg = MerchantFrameBg {
}
GetPortrait = defined @SharedXML/PortraitFrame.lua:63
SetTitleFormatted = defined @SharedXML/PortraitFrame.lua:40
NineSlice = Frame {
}
TopTileStreaks = Texture {
}
SetPortraitToAsset = defined @SharedXML/PortraitFrame.lua:72
SetPortraitTextureSizeAndOffset = defined @SharedXML/PortraitFrame.lua:106
CloseButton = MerchantFrameCloseButton {
}
SetPortraitAtlasRaw = defined @SharedXML/PortraitFrame.lua:88
numTabs = 2
page = 1
selectedTab = 1
Inset = MerchantFrameInset {
}
}
(*temporary) = "BOTTOMRIGHT"
(*temporary) = -148
(*temporary) = 33
(*temporary) = "attempt to index global 'MerchantFrameBottomRightBorder' (a nil value)"
InitialWidth = 336
trace = defined @MerchantPlus/MerchantPlus.lua:29
BuybackDirty = false
Addon = {
GetOption = defined @MerchantPlus/MerchantPlus.lua:68
GetAceOption = defined @MerchantPlus/MerchantPlus.lua:78
Init = defined @MerchantPlus/MerchantPlus.lua:446
UpdateFrame = defined @MerchantPlus/MerchantPlus.lua:187
UpdateSort = defined @MerchantPlus/MerchantPlus.lua:327
ClearMerchantTaint = defined @MerchantPlus/MerchantPlus.lua:438

Line 243 of MerchantPlus.lua doesn't reference the MerchantFrameBottomRightBorder. Somehow you seem to have an older version of the addon loading, likely 10.1.0.0. Can you double check you don't have any extra content in your addons folder?

Looks like wowup downloaded an old version then. It since downloaded a new version and that seems to work. Seems like it's better to just go back to manually download addons these days.

Anyway, i'll close this since this is more a addon manager bug then anything else. But thanks for looking into it anywya?